If program paths (GCC installation, --sysroot, -B, etc) don't contain
ld.lld, whether -fuse-ld=lld succeeds depends on whether a PATH
directory contains ld.lld.
> error: invalid linker name in argument '-fuse-ld=lld'
This behavior is not suitable when we adopt the new strict behavior of
-### in D156363.
For some tests, append -B%S/Inputs/lld similar to D92028.
For others, use -fuse-ld=ld so that getDefaultLinker (instead of CLANG_DEFAULT_LINKER) is used. The complexity stems from CLANG_DEFAULT_LINKER.
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