Also apply WITH_LLD_AS_LD to build tools

Previously WITH_LLD_AS_LD installed LLD as /usr/bin/ld in the target
system, but still used the GNU BFD ld to link the binaries in that
target. LLD 4.0.0 can link the FreeBSD/amd64 world and kernel so use
LLD as the build-time linker as well when the knob is set.

Reviewed by:	dim
Relnotes:	Yes
Sponsored by:	The FreeBSD Foundation
Differential Revision:	https://reviews.freebsd.org/D9226

Makefile.inc1

@@ -516,7 +516,7 @@ TMAKE=		MAKEOBJDIRPREFIX=${OBJTREE} \
 # cross-tools stage
 XMAKE=		TOOLS_PREFIX=${WORLDTMP} ${BMAKE} \
 		TARGET=${TARGET} TARGET_ARCH=${TARGET_ARCH} \
-		MK_GDB=no MK_TESTS=no MK_LLD_AS_LD=no
+		MK_GDB=no MK_TESTS=no
 
 # kernel-tools stage
 KTMAKEENV=	INSTALL="sh ${.CURDIR}/tools/install.sh" \
@@ -1827,6 +1827,9 @@ _elftctools=	lib/libelftc \
 # cross-build on a FreeBSD 10 host:
 _elftctools+=	usr.bin/addr2line
 .endif
+.if ${MK_LLD_AS_LD} != "no"
+_lld=		usr.bin/clang/lld
+.endif
 .elif ${TARGET_ARCH} != ${MACHINE_ARCH} && ${MK_ELFTOOLCHAIN_BOOTSTRAP} != "no"
 # If cross-building with an external binutils we still need to build strip for
 # the target (for at least crunchide).
@@ -1851,6 +1854,7 @@ cross-tools: .MAKE .PHONY
     ${LOCAL_XTOOL_DIRS} \
     ${_clang_libs} \
     ${_clang} \
+    ${_lld} \
     ${_binutils} \
     ${_elftctools} \
     ${_dtrace_tools} \

lib/clang/libllvm/Makefile

@@ -1146,7 +1146,7 @@ SRCS_MIN+=	Transforms/Vectorize/SLPVectorizer.cpp
 SRCS_EXT+=	Transforms/Vectorize/Vectorize.cpp
 
 SRCS_ALL+=	${SRCS_MIN}
-.if !defined(TOOLS_PREFIX)
+.if !defined(TOOLS_PREFIX) || ${MK_LLD_AS_LD} != "no"
 SRCS_ALL+=	${SRCS_MIW}
 .endif
 .if ${MK_CLANG_EXTRAS} != "no"