Update the preprocessor regression tests to use the new driver if the new driver is built (FLANG_BUILD_NEW_DRIVER=On), otherwise the tests will still run using f18.
Summary of changes:
- Introduce %flang to the regression tests, which points to the new driver if it is built or otherwise points to f18
- Update all tests in flang/test/Preprocessing/ to use %flang
Differential Revision: https://reviews.llvm.org/D94805
Hew more closely to the C17 standard; perform macro replacement
of arguments to function-like macros unless they're being stringified
or pasted. Test with a model "assert" macro idiom that exposed
the problem.
Differential Revision: https://reviews.llvm.org/D87650
Faris Rehman