Hide -fuse-ld= not supported message for non-build targets

In some build configurations a warning about (an absolute path for)
-fuse-ld= not being supported by GCC was emitted during cleandir or
other non-build make targets.

For these non-build targets COMPILER_TYPE is set to "none" but we
treated the .else case for COMPILER_TYPE==clang as implying gcc.
Check instead for COMPILER_TYPE==gcc.

PR: 263913
Reported by: pstef
Reviewed by: pstef
MFC after: 2 weeks
Sponsored by: The FreeBSD Foundation