build-llvm: Bump to LLVM 20.1.0 RC 3 #1587

Job	Run time
prepare	4s
macos	2h 40m 27s
msys2 (mingw64)	2h 19m 26s
linux-asserts	0s
msys2 (clang64)	1h 56m 48s
linux	3h 10m 34s
linux-test-cross-build-ffmpeg	0s
linux-cross-aarch64	3h 19m 10s
linux-cross-windows (i686, ucrt)	3h 9m 7s
linux-cross-windows (x86_64, ucrt)	3h 13m 48s
linux-cross-windows (armv7, ucrt)	3h 7m 56s
linux-cross-windows (aarch64, ucrt)	3h 15m 29s
test-libcxx	0s
test-ffmpeg	0s
test-openmp	0s
test-compiler-rt	0s
test-toolchain (x86_64)	2m 12s
test-toolchain (i686)	2m 14s
upload-nightly	0s
	1d 2h 17m 15s

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