Compiletest normalization

[Firestar99]

Requires #380

To reduce compiletest stderr merge conflicts and reviewing effort:

• Removes line and column from rustc errors:
  

  rust-gpu/tests/compiletests/README.md

  Lines 86 to 87 in bbb1919

  	* `// normalize-stderr-test "\.rs:\d+:\d+" -> ".rs:""` remove the line and column from error messages, eg. `--> path/to/some.rs:8:6`
  	* `// normalize-stderr-test "(\n)\d* *([ -])([\|\+\-\=])" -> "$1 $2$3""` remove the line number prefixing the source code snippet, does not touch `...`

• Removes OpLine from some tests