[libc++] Make `std::lock_guard` available with `_LIBCPP_HAS_NO_THREADS` #4832

Job	Run time
stage1 (generic-cxx03, clang-19, clang++-19)	8m 18s
stage1 (generic-cxx26, clang-19, clang++-19)	14m 19s
stage1 (generic-modules, clang-19, clang++-19)	10m 54s
stage1 (generic-gcc, gcc-14, g++-14)	19m 54s
windows (clang-cl-dll, false)	9m 57s
windows (clang-cl-static, false)	9m 53s
stage2 (generic-cxx11, clang-19, clang++-19)	8m 12s
windows (clang-cl-no-vcruntime, false)	9m 54s
stage2 (generic-cxx14, clang-19, clang++-19)	8m 11s
windows (clang-cl-debug, false)	9m 55s
stage2 (generic-cxx17, clang-19, clang++-19)	8m 7s
windows (clang-cl-static-crt, false)	9m 53s
stage2 (generic-cxx20, clang-19, clang++-19)	8m 6s
windows (mingw-dll, true)	9m 53s
stage2 (generic-cxx23, clang-19, clang++-19)	10m 39s
windows (mingw-static, true)	9m 54s
stage2 (generic-gcc-cxx11, gcc-14, g++-14)	7m 40s
windows (mingw-dll-i686, true)	9m 54s
stage2 (generic-cxx23, clang-17, clang++-17)	8m 21s
stage2 (generic-cxx26, clang-18, clang++-18)	10m 21s
stage3	1s
	3h 22m 16s

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