Merge pull request rust-lang#273 from MikaelUrankar/freebsd_arm

FreeBSD arm needs clear_cache.c

Author: alexcrichton

build.rs

@@ -311,6 +311,10 @@ mod c {
                 ],
             );
 
+            if target_os == "freebsd" {
+                sources.extend(&["clear_cache.c"]);
+            }
+            
             // First of all aeabi_cdcmp and aeabi_cfcmp are never called by LLVM.
             // Second are little-endian only, so build fail on big-endian targets.
             // Temporally workaround: exclude these files for big-endian targets.