toplevel.mk: unexport ARCH, it ends up in CONFIG_ARCH if defined and messes the buildroot up

SVN-Revision: 32663

include/toplevel.mk

@@ -32,7 +32,7 @@ unexport P4PORT P4USER P4CONFIG P4CLIENT
 # prevent user defaults for quilt from interfering
 unexport QUILT_PATCHES QUILT_PATCH_OPTS
 
-unexport C_INCLUDE_PATH CROSS_COMPILE
+unexport C_INCLUDE_PATH CROSS_COMPILE ARCH
 
 # prevent distro default LPATH from interfering
 unexport LPATH