port the relevant clang CodeGen tests to zig in order to find C ABI bugs #10810

https://github.com/llvm/llvm-project/tree/release/14.x/clang/test/CodeGen

This issue is to go through these tests one by one, identify any that are worth porting to zig, and add them to our test suite.

The main purpose of this is to identify bugs in Zig's handling of C ABI.

Marking this as "bug" because I'm 100% confident it will find at least 1 bug.

Alternative path to solve this issue:

• add Aro as a C frontend #10795
• Copy the tests into zig's test suite without modifications and get them all passing.