Build LLDB as part of wasi-sdk (#596) #1098

Job	Run time
Build arm64-macos	31m 31s
Build x86_64-windows	3h 32m 51s
Build x86_64-macos	15m 17s
Build arm64-windows	2h 24m 50s
Build arm64-linux	1h 44m 52s
Build only sysroot - exceptions	17m 18s
Build x86_64-linux	2h 23m 14s
Build only sysroot - default	17m 48s
Finalize wasi-sdk artifacts	10m 13s
Test standalone toolchain	3m 59s
	11h 41m 53s

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