Add WITH_LLD_AS_LD build knob

If set it installs LLD as /usr/bin/ld.  LLD (as of version 3.9) is not
capable of linking the world and kernel, but can self-host and link many
substantial applications. GNU ld continues to be used for the world and
kernel build, regardless of how this knob is set.

It is on by default for arm64, and off for all other CPU architectures.

Sponsored by:	The FreeBSD Foundation

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_GDB=no MK_TESTS=no MK_LLD_AS_LD=no
 
 # kernel-tools stage
 KTMAKEENV=	INSTALL="sh ${.CURDIR}/tools/install.sh" \

gnu/usr.bin/binutils/ld/Makefile

@@ -49,7 +49,9 @@ CLEANFILES+=	ldemul-list.h stringify.sed
 
 FILES=		${LDSCRIPTS:S|^|ldscripts/|}
 FILESDIR=	${SCRIPTDIR}
+.if ${MK_LLD_AS_LD} == "no"
 LINKS=		${BINDIR}/ld.bfd ${BINDIR}/ld
+.endif
 
 HOST=		${TARGET_TUPLE}
 LIBSEARCHPATH=	\"=/lib\":\"=/usr/lib\"

share/mk/src.opts.mk

@@ -250,6 +250,11 @@ __DEFAULT_YES_OPTIONS+=LLVM_LIBUNWIND
 .else
 __DEFAULT_NO_OPTIONS+=LLVM_LIBUNWIND
 .endif
+.if ${__T} == "aarch64"
+__DEFAULT_YES_OPTIONS+=LLD_AS_LD
+.else
+__DEFAULT_NO_OPTIONS+=LLD_AS_LD
+.endif
 .if ${__T} == "aarch64" || ${__T} == "amd64"
 __DEFAULT_YES_OPTIONS+=LLD LLDB
 .else

tools/build/options/WITHOUT_LLD_AS_LD

@@ -0,0 +1,2 @@
+.\" $FreeBSD$
+Set to use GNU binutils ld as the system linker, instead of LLVM's LLD.

tools/build/options/WITH_LLD_AS_LD

@@ -0,0 +1,2 @@
+.\" $FreeBSD$
+Set to use LLVM's LLD as the system linker, instead of GNU binutils ld.

usr.bin/clang/lld/Makefile

@@ -1,10 +1,15 @@
 # $FreeBSD$
 
+.include <src.opts.mk>
+
 LLVM_SRCS=	${SRCTOP}/contrib/llvm
 LLD_SRCS=	${LLVM_SRCS}/tools/lld
 
 PROG_CXX=	ld.lld
 MAN=
+.if ${MK_LLD_AS_LD} != "no"
+SYMLINKS=	${PROG_CXX} ${BINDIR}/ld
+.endif
 
 CFLAGS+=	-I${LLD_SRCS}/include
 CFLAGS+=	-I${.OBJDIR}