Use clang-cl instead of cl to build jsglue.cpp

[jdm]

running: "C:\\Program Files (x86)\\Microsoft Visual Studio\\2017\\BuildTools\\VC\\Tools\\MSVC\\14.16.27023\\bin\\HostX64\\x64\\cl.exe" "-nologo" "-MD" "-Z7" "-Brepro" "-I" "C:\\Users\\task_1582275861\\repo\\target\\debug\\build\\mozjs_sys-0e161224f0a4af5f\\out\\build\\dist/include" "-I" "C:\\Users\\task_1582275861\\repo\\target\\debug\\build\\mozjs_sys-0e161224f0a4af5f\\out\\build\\js/src" "-W4" "-FI" "C:\\Users\\task_1582275861\\repo\\target\\debug\\build\\mozjs_sys-0e161224f0a4af5f\\out\\build/js/src/js-confdefs.h" "-DRUST_BINDGEN" "-DSTATIC_JS_API" "-DWIN32" "-D_CRT_USE_BUILTIN_OFFSETOF" "-FoC:\\Users\\task_1582275861\\repo\\target\\debug\\build\\mozjs_sys-0e161224f0a4af5f\\out\\build\\glue\\src/jsglue.o" "-c" "src/jsglue.cpp"

CI shows that we're using the wrong compiler executable.