Should not include MSVC config by default on Windows

[Milerius]

Hello i'm trying to compile on windows i'm using both (clang / clang-cl)

folly/CMakeLists.txt

Line 107 in 0006ae9

include(FollyCompilerMSVC)

This config give the following error respectively:

clang:

Cannot get compiler information:
	Compiler exited with error code 1: C:\ProgramData\scoop\shims\clang++.exe -xc++ /EHs /GF /Zc:referenceBinding /Zc:rvalueCast /Zc:implicitNoexcept /Zc:strictStrings /Zc:threadSafeInit /Zc:throwingNew /permissive- /std:c++latest /wd4191 /wd4291 /wd4309 /wd4310 /wd4366 /wd4587 /wd4592 /wd4628 /wd4723 /wd4724 /wd4868 /wd4996 /wd4068 /wd4091 /wd4146 /wd4800 /wd4018 /wd4365 /wd4388 /wd4389 /wd4100 /wd4459 /wd4505 /wd4701 /wd4702 /wd4061 /wd4127 /wd4200 /wd4201 /wd4296 /wd4316 /wd4324 /wd4355 /wd4371 /wd4435 /wd4514 /wd4548 /wd4571 /wd4574 /wd4582 /wd4583 /wd4619 /wd4623 /wd4625 /wd4626 /wd4643 /wd4647 /wd4668 /wd4706 /wd4710 /wd4711 /wd4714 /wd4820 /wd5026 /wd5027 /wd5031 /wd5045 /we4099 /we4129 /we4566 -std=gnu++17 -fpch-preprocess -v -dD -E
	clang version 9.0.0 (tags/RELEASE_900/final)
	Target: x86_64-pc-windows-msvc
	Thread model: posix
	InstalledDir: C:\ProgramData\scoop\apps\llvm\current\bin
	clang++: fatal error: no such file or directory: '/EHs'

clang-cl

Cannot get compiler information:
	Compiler exited with error code 1: C:\Program Files\LLVM\bin\clang-cl.exe -xc++ -/D_WINDOWS /W3 /GR /EHsc /MDd /Zi /Ob0 /Od /RTC1 /W4 /permissive- 4987 /Zi /FS /DEBUG /Od /MDd /Oy- /EHs /GF /Zc:referenceBinding /Zc:rvalueCast /Zc:implicitNoexcept /Zc:strictStrings /Zc:threadSafeInit /Zc:throwingNew /std:c++latest /wd4191 /wd4291 /wd4309 /wd4310 /wd4366 /wd4587 /wd4592 /wd4628 /wd4723 /wd4724 /wd4868 /wd4996 /wd4068 /wd4091 /wd4146 /wd4800 /wd4018 /wd4365 /wd4388 /wd4389 /wd4100 /wd4459 /wd4505 /wd4701 /wd4702 /wd4061 /wd4127 /wd4200 /wd4201 /wd4296 /wd4316 /wd4324 /wd4355 /wd4371 /wd4435 /wd4514 /wd4548 /wd4571 /wd4574 /wd4582 /wd4583 /wd4619 /wd4623 /wd4625 /wd4626 /wd4643 /wd4647 /wd4668 /wd4706 /wd4710 /wd4711 /wd4714 /wd4820 /wd5026 /wd5027 /wd5031 /wd5045 /we4099 /we4129 /we4566 -std:c++17 -fpch-preprocess -v -dD -E
	clang-cl: warning: unknown argument ignored in clang-cl: '-xc++' [-Wunknown-argument]
	clang-cl: warning: unknown argument ignored in clang-cl: '-fpch-preprocess' [-Wunknown-argument]
	clang-cl: warning: unknown argument ignored in clang-cl: '-dD' [-Wunknown-argument]
	clang version 8.0.1 (tags/RELEASE_801/final)
	Target: x86_64-pc-windows-msvc
	Thread model: posix
	InstalledDir: C:\Program Files\LLVM\bin
	clang-cl: error: no such file or directory: '4987'