macos updates

* try some macos travis stuff
 * put c in the link libs for macos since we always link with libSystem
 * for non-native targets on macos, allow runtime symbol resolution
   - it's causing an infinite loop in LLD.
 * for macos, always build compiler_rt and turn on LinkOnce because
   compiler_rt on darwin is missing some stuff.

src/codegen.cpp

@@ -139,6 +139,7 @@ CodeGen *codegen_create(Buf *root_src_path, const ZigTarget *target, OutType out
         g->zig_target.os == ZigLLVM_IOS)
     {
         g->libc_link_lib = create_link_lib(buf_create_from_str("c"));
+        g->link_libs_list.append(g->libc_link_lib);
     }
 
     return g;