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.

libc/calls/struct/dirent.h

@@ -10,5 +10,8 @@ struct dirent {      /* linux getdents64 abi */
   char d_name[256];  /* NUL-terminated basename */
 };
 
+struct dirstream;
+typedef struct dirstream DIR;
+
 #endif /* !(__ASSEMBLER__ + __LINKER__ + 0) */
 #endif /* COSMOPOLITAN_LIBC_CALLS_STRUCT_DIRENT_H_ */