The "isysroot" method for building world with clang.

First of all, Makefile.inc1 is modified to build the clang libraries and
binaries during the cross-tools stage, iff CC=clang.

We basically adjust WMAKEENV, which applies to the world stage, and
LIB32FLAGS, which optionally applies to 32-bit world stage, to add
-isysroot, -B and -L options, so the compiler looks under ${WORLDTMP}
for its headers, startup objects and libraries.

We also need to create symlinks from ${WORLDTMP}/usr/bin/as and ld to
${WORLDTMP}/usr/lib, since the -B option in clang is not additive, and
is used both for finding CRT startup objects and for finding the
assembler and linker.


diff --git a/Makefile.inc1 b/Makefile.inc1
index d2581c5..c31eba9 100644
--- a/Makefile.inc1
+++ b/Makefile.inc1
@@ -257,6 +257,10 @@ WMAKEENV=	${CROSSENV} \
 		VERSION="${VERSION}" \
 		INSTALL="sh ${.CURDIR}/tools/install.sh" \
 		PATH=${TMPPATH}
+.if ${CC:T:Mclang} == "clang"
+WMAKEENV+=	CC="${CC} -isysroot ${WORLDTMP} -B${WORLDTMP}/usr/lib/ -L${WORLDTMP}/usr/lib/" \
+		CXX="${CXX} -isysroot ${WORLDTMP} -B${WORLDTMP}/usr/lib/ -L${WORLDTMP}/usr/lib/"
+.endif
 .if ${MK_CDDL} == "no"
 WMAKEENV+=	NO_CTF=1
 .endif
@@ -289,8 +293,11 @@ LIB32WMAKEENV=	MACHINE=powerpc MACHINE_ARCH=powerpc \
 .endif
 
 
-LIB32FLAGS=	-m32 ${LIB32CPUFLAGS} -DCOMPAT_32BIT \
-		-isystem ${LIB32TMP}/usr/include/ \
+LIB32FLAGS=	-m32 ${LIB32CPUFLAGS} -DCOMPAT_32BIT
+.if ${CC:T:Mclang} == "clang"
+LIB32FLAGS+=	-isysroot ${LIB32TMP}/
+.endif
+LIB32FLAGS+=	-isystem ${LIB32TMP}/usr/include/ \
 		-L${LIB32TMP}/usr/lib32 \
 		-B${LIB32TMP}/usr/lib32
 
@@ -440,6 +447,11 @@ everything:
 	@echo "--------------------------------------------------------------"
 	@echo ">>> stage 4.4: building everything"
 	@echo "--------------------------------------------------------------"
+.if ${CC:T:Mclang} == "clang"
+	# mergemaster goes through this but those files do not exist
+	[ ! -e ${WORLDTMP}/usr/bin/as ] || ln -sf ${WORLDTMP}/usr/bin/as ${WORLDTMP}/usr/lib/as
+	[ ! -e ${WORLDTMP}/usr/bin/ld ] || ln -sf ${WORLDTMP}/usr/bin/ld ${WORLDTMP}/usr/lib/ld
+.endif
 	${_+_}cd ${.CURDIR}; ${WMAKE} par-all
 .if defined(LIB32TMP)
 build32:
@@ -453,6 +465,12 @@ build32:
 	mtree -deU -f ${.CURDIR}/etc/mtree/BSD.include.dist \
 	    -p ${LIB32TMP}/usr/include >/dev/null
 	mkdir -p ${WORLDTMP}
+.if ${CC:T:Mclang} == "clang"
+	# relink /usr/bin/{as,ld} to the lib32 tmp so the -B can pick up
+	# the /usr/bin/ld and /usr/bin/as
+	ln -sf ${WORLDTMP}/usr/bin/as ${LIB32TMP}/usr/lib32/as
+	ln -sf ${WORLDTMP}/usr/bin/ld ${LIB32TMP}/usr/lib32/ld
+.endif
 	ln -sf ${.CURDIR}/sys ${WORLDTMP}
 .if ${MK_KERBEROS} != "no"
 .for _t in obj depend all
@@ -1078,8 +1096,15 @@ _kgzip=		usr.sbin/kgzip
 .endif
 .endif
 
+.if ${CC:T:Mclang} == "clang"
+_clang=		usr.bin/clang
+_clang_libs=	lib/clang
+.endif
+
 cross-tools:
 .for _tool in \
+    ${_clang_libs} \
+    ${_clang} \
     gnu/usr.bin/binutils \
     gnu/usr.bin/cc \
     usr.bin/xlint/lint1 usr.bin/xlint/lint2 usr.bin/xlint/xlint \