If I write:

//@ only-windows
//@ ignore-windows-gnu // or just ignore-gnu

Then gnullvm will be also excluded. There are few things (like CFGuad) that will probably never work with mingw-w64+GNU targets but are supported on mingw-w64+LLVM (not yet within Rust).
Using //@ only-windows-gnullvm won't be an option because it would disable the test for *-windows-msvc.

One idea I can think of is to add $ character that means end of the line, just like in regex. So //@ ignore-windows-gnu$ would skip all *-windows-gnu targets from the given test but keep *-windows-gnullvm targets.

Originally posted by @mati865 in #128602
cc @jieyouxu