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

share/mk/bsd.sys.mk

@@ -326,7 +326,7 @@ LDFLAGS+=	--ld-path=${LD:[1]:S/^ld.//1W}
 .else
 LDFLAGS+=	-fuse-ld=${LD:[1]:S/^ld.//1W}
 .endif
-.else
+.elif ${COMPILER_TYPE} == "gcc"
 # GCC does not support an absolute path for -fuse-ld so we just print this
 # warning instead and let the user add the required symlinks.
 # However, we can avoid this warning if -B is set appropriately (e.g. for