[LLD][Cygwin] Implement --dll-search-prefix (#143263)
GCC on Cygwin environment invokes linker with passing
`--dll-search-prefix=cyg`.
Implementing this option makes lld-mingw invokable by `gcc -fuse-ld=lld`.
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Co-authored-by: jeremyd2019 <github@jdrake.com>
