Cannot build for `Windows 10`

[y-71]

failed to build on windows 10

  --- stderr
  Reticulating splines...
  Finished reading 60 moz.build files in 0.09s
  Read 0 gyp files in parallel contributing 0.00s to total wall time
  Processed into 224 build config descriptors in 0.10s
  RecursiveMake backend executed in 0.45s
    161 total backend files; 161 created; 0 updated; 0 unchanged; 0 deleted; 6 -> 38 Makefile
  Total wall time: 0.70s; CPU time: 0.47s; Efficiency: 67%; Untracked: 0.07s
  D:/Dev/mozjs/mozjs/intl/icu/source/common/unistr.cpp(1979,13): warning: unused function 'uprv_UnicodeStringDummy' [-Wunused-function]
  static void uprv_UnicodeStringDummy(void) {
              ^
  1 warning generated.

  error occurred: Command "C:\\Program Files (x86)\\Microsoft Visual Studio\\2017\\Community\\VC\\Tools\\MSVC\\14.16.27023\\bin\\HostX64\\x64\\cl.exe" "-nologo" "-MD" "-Z7" "-Brepro" "-I" "D:\\dev\\mozjs\\target\\debug\\build\\mozjs_sys-a5bb08c3318f88fa\\out\\build\\dist/include" "-I" "D:\\dev\\mozjs\\target\\debug\\build\\mozjs_sys-a5bb08c3318f88fa\\out\\build\\js/src" "-W4" "-FI" "D:\\dev\\mozjs\\target\\debug\\build\\mozjs_sys-a5bb08c3318f88fa\\out\\build/js/src/js-confdefs.h" "-DRUST_BINDGEN" "-DSTATIC_JS_API" "-DWIN32" "-D_CRT_USE_BUILTIN_OFFSETOF" "-std:c++17" "-FoD:\\dev\\mozjs\\target\\debug\\build\\mozjs_sys-a5bb08c3318f88fa\\out\\build\\glue\\src/jsglue.o" "-c" "src/jsglue.cpp" with args "cl.exe" did not execute successfully (status code exit code: 2).

[jdm]

I suspect the issue here is that cl.exe from MSVC is being used instead of clang. Spidermonkey no longer supports building with the MSVC compiler. What if you run with CC=cl-clang and CXX=cl-clang?