LINKER_VERSION: Support external binutils.

The ports binutils stores the version in the 5th word so just look for
a version using a pattern instead.

Reported by:	rpokala
MFC after:	2 weeks
Sponsored by:	Dell EMC Isilon

share/mk/bsd.linker.mk

@@ -48,7 +48,7 @@ _ld_version!=	${${ld}} --version 2>/dev/null | head -n 1 || echo none
 .endif
 .if ${_ld_version:[1..2]} == "GNU ld"
 ${X_}LINKER_TYPE=	binutils
-_v=	${_ld_version:[3]}
+_v=	${_ld_version:M[1-9].[0-9]*:[1]}
 .elif ${_ld_version:[1]} == "LLD"
 ${X_}LINKER_TYPE=	lld
 _v=	${_ld_version:[2]}