[Build Error] "Multiple definition of 'main' " while building IL2CPP

We have two building machines, with almost exactly the same setup and configuration, trying to build exactly the same code. One of them succeeds, the other don't.

Spoiler: Err1

Failed running C:\2019.1.3f1\Editor\Data\il2cpp/build/il2cpp.exe --convert-to-cpp --emit-null-checks --enable-array-bounds-check --dotnetprofile="unityaot" --compile-cpp --libil2cpp-static --platform="Android" --architecture="ARMv7" --configuration="Release" --outputpath="C:\repo\headsUp\Temp\StagingArea\assets\bin\Data\Native\armeabi-v7a\libil2cpp.so" --cachedirectory="C:\repo\headsUp\Assets\..\Library\il2cpp_android_armeabi-v7a/il2cpp_cache" --additional-include-directories="C:\2019.1.3f1\Editor\Data\PlaybackEngines\AndroidPlayer/Tools\bdwgc/include" --additional-include-directories="C:\2019.1.3f1\Editor\Data\PlaybackEngines\AndroidPlayer/Tools\libil2cpp/include" --tool-chain-path="C:/2019.1.3f1/Editor/Data/PlaybackEngines/AndroidPlayer/NDK" --profiler-report --map-file-parser=C:/2019.1.3f1/Editor/Data/Tools/MapFileParser/MapFileParser.exe --directory=C:/repo/headsUp/Temp/StagingArea/assets/bin/Data/Managed --generatedcppdir=C:/repo/headsUp/Temp/StagingArea/Il2Cpp/il2cppOutput

stdout:

Building libil2cpp.so with AndroidToolChain

Output directory: C:\repo\headsUp\Temp\StagingArea\assets\bin\Data\Native\armeabi-v7a

Cache directory: C:\repo\headsUp\Library\il2cpp_android_armeabi-v7a\il2cpp_cache

ObjectFiles: 244 of which compiled: 0

Total compilation time: 439 milliseconds.

il2cpp.exe didn't catch exception: Unity.IL2CPP.Building.BuilderFailedException: C:\2019.1.3f1\Editor\Data\PlaybackEngines\AndroidPlayer\NDK\toolchains\llvm\prebuilt\windows-x86_64\bin\clang++ @"C:\Users\Ja\AppData\Local\Temp\tmpBCC7.tmp" -o "C:\repo\headsUp\Library\il2cpp_android_armeabi-v7a\il2cpp_cache\linkresult_DED600FCD620CD5C8D5EA19A704AFBF0\libil2cpp.so" -shared -Wl,-soname,libil2cpp.so -Wl,--no-undefined -Wl,-z,noexecstack -Wl,--gc-sections -Wl,--build-id --sysroot "C:\2019.1.3f1\Editor\Data\PlaybackEngines\AndroidPlayer\NDK\platforms\android-16\arch-arm" -gcc-toolchain "C:\2019.1.3f1\Editor\Data\PlaybackEngines\AndroidPlayer\NDK\toolchains\arm-linux-androideabi-4.9\prebuilt\windows-x86_64" -target armv7-none-linux-androideabi -Wl,--wrap,sigaction -L "C:\2019.1.3f1\Editor\Data\PlaybackEngines\AndroidPlayer\NDK\sources\cxx-stl\gnu-libstdc++\4.9\libs\armeabi-v7a" -lgnustl_static -llog -rdynamic -fuse-ld=gold.exe



C:\2019.1.3f1\Editor\Data\PlaybackEngines\AndroidPlayer\NDK\toolchains\arm-linux-androideabi-4.9\prebuilt\windows-x86_64/lib/gcc/arm-linux-androideabi/4.9.x/../../../../arm-linux-androideabi/bin\ld.gold.exe: error: C:/repo/headsUp/Library/il2cpp_android_armeabi-v7a/il2cpp_cache/B2890308F646519949D7EBBA6574BD0A.o: multiple definition of 'main'

C:\2019.1.3f1\Editor\Data\PlaybackEngines\AndroidPlayer\NDK\toolchains\arm-linux-androideabi-4.9\prebuilt\windows-x86_64/lib/gcc/arm-linux-androideabi/4.9.x/../../../../arm-linux-androideabi/bin\ld.gold.exe: C:/repo/headsUp/Library/il2cpp_android_armeabi-v7a/il2cpp_cache/9D8CBB5FEC3BCB14189EBD10EE7C22BE.o: previous definition here

clang++.exe: error: linker command failed with exit code 1 (use -v to see invocation)





w Unity.IL2CPP.Building.CppProgramBuilder.PostprocessObjectFiles(HashSet`1 objectFiles, CppToolChainContext toolChainContext)

w Unity.IL2CPP.Building.CppProgramBuilder.Build(IBuildStatistics& statistics)

w il2cpp.Program.DoRun(String[] args)

w il2cpp.Program.Run(String[] args)

w il2cpp.Program.Main(String[] args)

UnityEngine.Debug:LogError(Object)
UnityEditorInternal.Runner:RunProgram(Program, String, String, String, CompilerOutputParserBase) (at C:/buildslave/unity/build/Editor/Mono/BuildPipeline/BuildUtils.cs:128)
UnityEditorInternal.Runner:RunManagedProgram(String, String, String, CompilerOutputParserBase, Action`1) (at C:/buildslave/unity/build/Editor/Mono/BuildPipeline/BuildUtils.cs:73)
UnityEditorInternal.IL2CPPBuilder:RunIl2CppWithArguments(List`1, Action`1, String) (at C:/buildslave/unity/build/Editor/Mono/BuildPipeline/Il2Cpp/IL2CPPUtils.cs:496)
UnityEditorInternal.IL2CPPBuilder:ConvertPlayerDlltoCpp(String, String, String, Boolean) (at C:/buildslave/unity/build/Editor/Mono/BuildPipeline/Il2Cpp/IL2CPPUtils.cs:477)
UnityEditorInternal.IL2CPPBuilder:Run() (at C:/buildslave/unity/build/Editor/Mono/BuildPipeline/Il2Cpp/IL2CPPUtils.cs:334)
UnityEditorInternal.IL2CPPUtils:RunIl2Cpp(String, String, IIl2CppPlatformProvider, Action`1, RuntimeClassRegistry) (at C:/buildslave/unity/build/Editor/Mono/BuildPipeline/Il2Cpp/IL2CPPUtils.cs:63)
UnityEngine.GUIUtilityrocessEvent(Int32, IntPtr)

Spoiler: Err 2

Exception: C:\2019.1.3f1\Editor\Data\il2cpp/build/il2cpp.exe did not run properly!
UnityEditorInternal.Runner.RunProgram (UnityEditor.Utils.Program p, System.String exe, System.String args, System.String workingDirectory, UnityEditor.Scripting.Compilers.CompilerOutputParserBase parser) (at C:/buildslave/unity/build/Editor/Mono/BuildPipeline/BuildUtils.cs:130)
UnityEditorInternal.Runner.RunManagedProgram (System.String exe, System.String args, System.String workingDirectory, UnityEditor.Scripting.Compilers.CompilerOutputParserBase parser, System.Action`1[T] setupStartInfo) (at C:/buildslave/unity/build/Editor/Mono/BuildPipeline/BuildUtils.cs:73)
UnityEditorInternal.IL2CPPBuilder.RunIl2CppWithArguments (System.Collections.Generic.List`1[T] arguments, System.Action`1[T] setupStartInfo, System.String workingDirectory) (at C:/buildslave/unity/build/Editor/Mono/BuildPipeline/Il2Cpp/IL2CPPUtils.cs:496)
UnityEditorInternal.IL2CPPBuilder.ConvertPlayerDlltoCpp (System.String inputDirectory, System.String outputDirectory, System.String workingDirectory, System.Boolean platformSupportsManagedDebugging) (at C:/buildslave/unity/build/Editor/Mono/BuildPipeline/Il2Cpp/IL2CPPUtils.cs:477)
UnityEditorInternal.IL2CPPBuilder.Run () (at C:/buildslave/unity/build/Editor/Mono/BuildPipeline/Il2Cpp/IL2CPPUtils.cs:334)
UnityEditorInternal.IL2CPPUtils.RunIl2Cpp (System.String tempFolder, System.String stagingAreaData, UnityEditorInternal.IIl2CppPlatformProvider platformProvider, System.Action`1[T] modifyOutputBeforeCompile, UnityEditor.RuntimeClassRegistry runtimeClassRegistry) (at C:/buildslave/unity/build/Editor/Mono/BuildPipeline/Il2Cpp/IL2CPPUtils.cs:63)
UnityEditor.Android.PostProcessor.Tasks.RunIl2Cpp.Execute (UnityEditor.Android.PostProcessor.PostProcessorContext context) (at <563f4bbc342a4b6b88ae70c46cea610c>:0)
UnityEditor.Android.PostProcessor.PostProcessRunner.RunAllTasks (UnityEditor.Android.PostProcessor.PostProcessorContext context) (at <563f4bbc342a4b6b88ae70c46cea610c>:0)
UnityEditor.Android.PostProcessAndroidPlayer.PostProcess (UnityEditor.BuildTarget target, System.String stagingAreaData, System.String stagingArea, System.String playerPackage, System.String installPath, System.String companyName, System.String productName, UnityEditor.BuildOptions options, UnityEditor.RuntimeClassRegistry usedClassRegistry, UnityEditor.Build.Reporting.BuildReport report) (at <563f4bbc342a4b6b88ae70c46cea610c>:0)
UnityEditor.Android.AndroidBuildPostprocessor.PostProcess (UnityEditor.Modules.BuildPostProcessArgs args, UnityEditor.BuildProperties& outProperties) (at <563f4bbc342a4b6b88ae70c46cea610c>:0)
UnityEditor.PostprocessBuildPlayer.Postprocess (UnityEditor.BuildTargetGroup targetGroup, UnityEditor.BuildTarget target, System.String installPath, System.String companyName, System.String productName, System.Int32 width, System.Int32 height, UnityEditor.BuildOptions options, UnityEditor.RuntimeClassRegistry usedClassRegistry, UnityEditor.Build.Reporting.BuildReport report) (at C:/buildslave/unity/build/Editor/Mono/BuildPipeline/PostprocessBuildPlayer.cs:281)
UnityEngine.GUIUtilityrocessEvent(Int32, IntPtr)

Everything builds well when using 'mono' scripting backend, with exactly the same setup.
Was hoping anyone would think of any way to fix this, or to help diagnose the problem.