Peephole for simulated 32-bit regs #208

Job	Run time
abi-dump-setup	1m 23s
Test llvm,clang,libclc / Lit Tests (ubuntu-latest)	40m 18s
Build lldb / Lit Tests (ubuntu-latest)	21m 46s
Test llvm,clang,libclc / Lit Tests (windows-2019)	2m 24s
Test lld / Lit Tests (ubuntu-latest)	9m 21s
Build lldb / Lit Tests (windows-2019)	1m 53s
Test llvm,clang,libclc / Lit Tests (macOS-latest)	59m 22s
Test lld / Lit Tests (windows-2019)	2m 23s
Build lldb / Lit Tests (macOS-latest)	21m 59s
Test lld / Lit Tests (macOS-latest)	9m 53s
abi-dump (build-baseline)	33m 20s
abi-dump (build-latest)	32m 4s
abi-compare	34s
	3h 56m 40s

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