remove unused ARCH_GCC definitions

Author: jjallaire

src/Makevars

@@ -44,10 +44,8 @@ ifeq ($(USE_TBB),  Windows)
   ifeq ("$(WIN)", "64")
     # TBB defaults to ia32
     MAKE_ARGS += arch=intel64
-    ARCH_GCC=64
     ARCH_DIR=x64/
   else
-    ARCH_GCC=32
     ARCH_DIR=i386/
   endif