_cpp_find_file has 3 bool arguments, at most one of which is ever set.
Ripe for replacing with a 4-state enum. Also, this is C++, so
'typedef struct Foo Foo' is unnecessary.
* internal.h (typedef _cpp_file): Delete, unnecessary in C++.
(enum _cpp_find_file_kind): New.
(_cpp_find_file): Use it, not 3 bools.
* files.c (_cpp_find_file): Use _cpp_find_file_kind enum, not
bools.
(cpp_make_system_header): Break overly long line.
(_cpp_stack_include, _cpp_fake_include)
(_cpp_do_file_change, _cpp_compare_file_date, _cpp_has_header): Adjust.
* init.c (cpp_read_main): Adjust _cpp_find_file call.