To reproduce:
1. Open project
2. Build scene for WebGL

Expected: scene will be built without any errors
Actual: IL2CPP.exe crashes, an error is thrown:
'Exception: E:\Program Files\Unity 2017.2.0b3\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 setupStartInfo) (at C:/buildslave/unity/build/Editor/Mono/BuildPipeline/BuildUtils.cs:73)
UnityEditorInternal.IL2CPPBuilder.RunIl2CppWithArguments (System.Collections.Generic.List`1 arguments, System.Action`1 setupStartInfo, System.String workingDirectory) (at C:/buildslave/unity/build/Editor/Mono/BuildPipeline/Il2Cpp/IL2CPPUtils.cs:324)
UnityEditorInternal.IL2CPPBuilder.ConvertPlayerDlltoCpp (ICollection`1 userAssemblies, System.String outputDirectory, System.String workingDirectory) (at C:/buildslave/unity/build/Editor/Mono/BuildPipeline/Il2Cpp/IL2CPPUtils.cs:305)
UnityEditorInternal.IL2CPPBuilder.Run () (at C:/buildslave/unity/build/Editor/Mono/BuildPipeline/Il2Cpp/IL2CPPUtils.cs:151)
UnityEditorInternal.IL2CPPUtils.RunIl2Cpp (System.String stagingAreaData, IIl2CppPlatformProvider platformProvider, System.Action`1 modifyOutputBeforeCompile, UnityEditor.RuntimeClassRegistry runtimeClassRegistry, Boolean debugBuild) (at C:/buildslave/unity/build/Editor/Mono/BuildPipeline/Il2Cpp/IL2CPPUtils.cs:41)
UnityEditor.WebGL.WebGlBuildPostprocessor.CompileBuild (BuildPostProcessArgs args) (at /Users/builduser/buildslave/unity/build/PlatformDependent/WebGL/Extensions/Unity.WebGL.extensions/BuildPostprocessor.cs:340)
UnityEditor.WebGL.WebGlBuildPostprocessor.PostProcess (BuildPostProcessArgs args) (at /Users/builduser/buildslave/unity/build/PlatformDependent/WebGL/Extensions/Unity.WebGL.extensions/BuildPostprocessor.cs:893)
UnityEditor.PostprocessBuildPlayer.Postprocess (BuildTargetGroup targetGroup, BuildTarget target, System.String installPath, System.String companyName, System.String productName, Int32 width, Int32 height, BuildOptions options, UnityEditor.RuntimeClassRegistry usedClassRegistry, UnityEditor.BuildReporting.BuildReport report) (at C:/buildslave/unity/build/Editor/Mono/BuildPipeline/PostprocessBuildPlayer.cs:271)
UnityEngine.GUIUtility:ProcessEvent(Int32, IntPtr)'

Reproducible: 2017.1.0b6, 2017.1.0f3, 2017.2.0b3
Not reproducible: 5.6.1f1, 5.6.2p2

Note: reproducible only on Windows 7 (also tested on Windows 10, OSX 10.12.5)