The dependency output for header unit modules is based on the absolute
pathname of the header file, but that's not something that a makefile can
portably refer to. This patch adds a .c++-header-unit target based on the
header name relative to an element of the include path.
libcpp/ChangeLog:
* internal.h (_cpp_get_file_dir): Declare.
* files.cc (_cpp_get_file_dir): New fn.
* mkdeps.cc (make_write): Use it.
gcc/testsuite/ChangeLog:
* g++.dg/modules/dep-4.H: New test.
7b8b96a327