Get codebase completely working with LLVM

You can now build Cosmopolitan with Clang:

    make -j8 MODE=llvm
    o/llvm/examples/hello.com

The assembler and linker code is now friendly to LLVM too.
So it's not needed to configure Clang to use binutils under
the hood. If you love LLVM then you can now use pure LLVM.

tool/build/ar.c

@@ -82,7 +82,7 @@ struct Header {
 static void MakeHeader(struct Header *h, const char *name, int ref, int mode,
                        int size) {
   size_t n;
-  char buf[21];
+  char buf[24];
   memset(h, ' ', sizeof(*h));
   n = strlen(name);
   memcpy(h->name, name, n);