Support for libc++ std modules #1145

Job	Run time
prepare	4s
linux	18m 36s
macos	2h 5m 28s
linux-asserts	0s
msys2 (clang64)	34m 5s
linux-test-cross-build-ffmpeg	0s
linux-cross-aarch64	13m 50s
linux-cross-windows (i686, ucrt)	6m 4s
linux-cross-windows (x86_64, ucrt)	6m 2s
linux-cross-windows (aarch64, ucrt)	5m 48s
test-compiler-rt	0s
test-libcxx	0s
test-openmp	0s
test-ffmpeg	0s
test-toolchain (x86_64)	1m 39s
test-toolchain (i686)	1m 40s
upload-nightly	0s
	3h 33m 16s

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