https://gcc.gnu.org/ml/gcc-patches/2019-08/msg01971.html
* internal.h (enum include_type): Add IT_MAIN, IT_DIRECTIVE_HWM,
IT_HEADER_HWM.
(_cpp_stack_file): Take include_type, not a bool.
* files.c (_cpp_find_file): Refactor to not hide an if inside a
for conditional.
(should_stack_file): Break apart to ...
(is_known_idempotent_file, has_unique_contents): ... these.
(_cpp_stack_file): Replace IMPORT boolean with include_type enum.
Refactor to use new predicates. Do linemap compensation here ...
(_cpp_stack_include): ... not here.
* init.c (cpp_read_main_file): Pass IT_MAIN to _cpp_stack_file.
From-SVN: r275034
b0d11f1ed6