Supersedes D80225. Add -fld-path= to avoid strange target specific
prefixes and make -fuse-ld= focus on its intended job: "linker flavor".
-fuse-ld= and -fld-path= can be composed, e.g. `-fuse-ld=lld -fld-path=/usr/bin/ld.lld`
The driver can provide additional linker options based on the flavor `lld`, but it should not do fragile
flavor checking with -fld-path=