On Windows, the winerror.h header defines WAIT_TIMEOUT as a macro.
This introduces a fragile dependency on header inclusion order: if Windows headers happen to be included before using WAIT_TIMEOUT, the preprocessor expands it into a numeric literal, causing syntax errors.
Rename the variable to TEST_WAIT_TIMEOUT to remove this fragility and avoid the collision entirely.
Split from #34448.
Similar to #34454.