update llvm toolchain repo (#131) #729

Job	Run time
coverage	3m 15s
buildifier	14s
test (gcc)	2m 49s
build (--config=clang-format)	2m 23s
test (gcc, asan)	2m 42s
build (--config=clang-tidy)	5m 49s
test (gcc, tsan)	2m 51s
build (--config=verbose-clang-tidy)	6m 59s
test (gcc, ubsan)	2m 44s
build (--compilation_mode=opt)	3m 21s
test (clang)	3m 12s
test (clang, asan)	3m 17s
test (clang, tsan)	3m 9s
test (clang, ubsan)	3m 6s
	45m 51s

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