Allow to set directory for as backends from the outside.

--- cctools-855/as/driver.c.orig	2014-04-05 00:42:22.000000000 +0200
+++ cctools-855/as/driver.c	2014-11-13 13:07:09.000000000 +0100
@@ -365,7 +365,11 @@
 	/*
 	 * If this assembler exist try to run it else print an error message.
 	 */
+#ifndef ASLIBEXECDIR
 	as = makestr(prefix, LIB, arch_name, AS, NULL);
+#else
+	as = makestr(ASLIBEXECDIR, arch_name, AS, NULL);
+#endif
 	new_argv = allocate((argc + 1) * sizeof(char *));
 	new_argv[0] = as;
 	j = 1;
@@ -387,6 +391,9 @@
 	    else
 		exit(1);
 	}
+#ifdef ASLIBEXECDIR
+	as_local = "";
+#else
 	as_local = makestr(prefix, LOCALLIB, arch_name, AS, NULL);
 	new_argv[0] = as_local;
 	if(access(as_local, F_OK) == 0){
@@ -396,10 +403,12 @@
 	    else
 		exit(1);
 	}
+#endif
 	printf("%s: assembler (%s or %s) for architecture %s not installed\n",
 	       progname, as, as_local, arch_name);
 	arch_flags = get_arch_flags();
 	count = 0;
+#ifndef ASLIBEXECDIR
 	for(i = 0; arch_flags[i].name != NULL; i++){
 	    as = makestr(prefix, LIB, arch_flags[i].name, AS, NULL);
 	    if(access(as, F_OK) == 0){
@@ -420,6 +429,7 @@
 		}
 	    }
 	}
+#endif
 	if(count == 0)
 	    printf("%s: no assemblers installed\n", progname);
 	exit(1);