xdev: Follow-up r325087: Need to build lib/clang before lld.

LLD needs headers generated by the full libllvm.

X-MFC-With:	r325087
MFC after:	2 weeks
Sponsored by:	Dell EMC Isilon

Makefile.inc1

@@ -2853,11 +2853,11 @@ _xb-build-tools: .PHONY
 	${CDBENV} ${MAKE} -f Makefile.inc1 ${NOFUN} build-tools
 
 XDEVDIRS= \
+    ${_clang_libs} \
     ${_lld} \
     ${_binutils} \
     ${_elftctools} \
     usr.bin/ar \
-    ${_clang_libs} \
     ${_clang} \
     ${_gcc}