* cppdefault.c (cpp_include_defaults):  Also search PREFIX_INCLUDE_DIR.
	* Makefile.in (includedir):  Rename to local_includedir.
	(includedir):  Define as $(prefix)/include.
	* config.in (PREFIX_INCLUDE_DIR):  New variable.
	* configure.in (PREFIX_INCLUDE_DIR):  Test for new variable.

From-SVN: r45884