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
If the label field is empty, and macro replacement occurs,
the rescanned text might be misclassified as a comment card
if it happens to begin with a C or a D. Insert a leading
space into these otherwise empty label fields.
Fixes https://bugs.llvm.org/show_bug.cgi?id=47173
