If we're using Clang as the compiler, use it as the assembler too.

Should fix issue reported by Floffy on IRC.

src/build/Common.gmake

@@ -169,10 +169,12 @@ CC		?=	gcc
 CCPRE	?= ${shell if [ `echo __clang__ | $(CC) -E - | grep -v '^\#'` != __clang__ ] ; then echo clang ; elif [ `echo __INTEL_COMPILER | $(CC) -E - | grep -v '^\#'` != __INTEL_COMPILER ] ; then echo icc ; else echo gcc ; fi}
 ifeq ($(CCPRE),clang)
  ifeq ($(CC),cc)
-  CXX	:=	c++
+  CXX	:= c++
+  AS	:= cc
  else
   ifeq ($(CC),clang)
-   CXX	:=	clang++
+   CXX	:= clang++
+   AS	:= clang
   endif
  endif
 endif