[Tinycc-devel] Support tinycc's assembler format

[John Nunley]

I am using QBE as a backend for a WIP Rust compiler. I intend for this 
compiler to be used in bootstrap environments; hence I am building it 
with TinyCC. FYI, TinyCC comes with a built-in assembler, which I 
planned to leverage here.

However, I encountered this error with TinyCC, when attempting to use it 
to compile:

```
/tmp/out.S:10: error: unknown opcode 'callq'
ci/test.sh: error on line 21: "$CC" /tmp/out.S ./src/libdozer.a -o /tmp/out
```

It looks like TinyCC's assembler does not support the 'callq' function. 
Would it be possible to add this?

Another option would be patching QBE to be able to support TinyCC's 
assembler format. But it looks like the opcode is the issue.