Need quoted value for assembler.

Author: grafikrobot

src/tools/clang-win.jam

@@ -169,6 +169,7 @@ rule init ( version ? : command * : options * )
                 : $(assembler)
                 : "$(linker:D)" "$(vsasmpath:D)"
                 : path-last ] ;
+            assembler = "$(assembler)" ;
 
             .notice "$(arch)-$(addr):" "using linker '$(linker)'" ;