Linking fails when targeting x86_64-apple-darwin for runtimes. The issue
is that LLD strictly assumes the target architecture be present in the tbd
files (which isn't always true). For example, when targeting x86_64h, it should
work with x86_64 because they are ABI compatible. This is also inline with what
An environment variable (which ld64 also supports) is also added to preserve the
existing behavior of strict architecture matching.