[asm] Allow block address operands in `asm inteldialect`

This makes the following program build with -masm=intel:

    int foo(int count) {
      asm goto ("dec %0; jb %l[stop]" : "+r" (count) : : : stop);
      return count;
    stop:
      return 0;
    }

It's also is another step towards merging EmitGCCInlineAsmStr() and
EmitMSInlineAsmStr().

Differential Revision: https://reviews.llvm.org/D114167