build-llvm: Bump to LLVM 19.1.2 #1396

Job	Run time
prepare	4s
linux	3h 0m 57s
msys2 (mingw64)	2h 10m 45s
linux-asserts	0s
macos	2h 26m 37s
msys2 (clang64)	1h 58m 41s
linux-test-cross-build-ffmpeg	0s
linux-cross-aarch64	3h 13m 54s
linux-cross-windows (i686, ucrt)	3h 8m 14s
linux-cross-windows (x86_64, ucrt)	3h 12m 21s
linux-cross-windows (armv7, ucrt)	3h 3m 54s
linux-cross-windows (aarch64, ucrt)	3h 9m 10s
test-openmp	0s
test-libcxx	0s
test-ffmpeg	0s
test-compiler-rt	0s
test-toolchain (x86_64)	2m 13s
test-toolchain (i686)	2m 6s
upload-nightly	0s
	1d 1h 28m 56s

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