Add basic bsd.linker.mk auto included from bsd.compiler.mk.

This will provide LINKER_TYPE and LINKER_VERSION.

MFC after:	2 weeks
Reviewed by:	emaste
Sponsored by:	Dell EMC Isilon
Differential Revision:	https://reviews.freebsd.org/D11308

share/mk/Makefile

@@ -33,6 +33,7 @@ FILES=	\
 	bsd.kmod.mk \
 	bsd.lib.mk \
 	bsd.libnames.mk \
+	bsd.linker.mk \
 	bsd.links.mk \
 	bsd.man.mk \
 	bsd.mkopt.mk \

share/mk/bsd.compiler.mk

@@ -194,4 +194,5 @@ ${var}.${${X_}_cc_hash}:=	${${var}}
 .endif	# ${cc} == "CC" || !empty(XCC)
 .endfor	# .for cc in CC XCC
 
+.include <bsd.linker.mk>
 .endif	# !target(__<bsd.compiler.mk>__)

share/mk/bsd.linker.mk

@@ -0,0 +1,33 @@
+# $FreeBSD$
+
+# Setup variables for the linker.
+#
+# LINKER_TYPE is the major type of linker. Currently binutils and lld support
+# automatic detection.
+#
+# LINKER_VERSION is a numeric constant equal to:
+#     major * 10000 + minor * 100 + tiny
+# It too can be overridden on the command line.
+#
+# This file may be included multiple times, but only has effect the first time.
+#
+
+.if !target(__<bsd.linker.mk>__)
+__<bsd.linker.mk>__:
+
+_ld_version!=	${LD} --version 2>/dev/null | head -n 1 || echo none
+.if ${_ld_version} == "none"
+.error Unable to determine linker type from LD=${LD}
+.endif
+.if ${_ld_version:[1..2]} == "GNU ld"
+LINKER_TYPE=	binutils
+_v=	${_ld_version:[3]}
+.elif ${_ld_version:[1]} == "LLD"
+LINKER_TYPE=	lld
+_v=	${_ld_version:[2]}
+.else
+.error Unknown linker from LD=${LD}: ${_ld_version}
+.endif
+LINKER_VERSION!=echo "${_v:M[1-9].[0-9]*}" | awk -F. '{print $$1 * 10000 + $$2 * 100 + $$3;}'
+
+.endif	# !target(__<bsd.linker.mk>__)