* cppdefault.c (cpp_EXEC_PREFIX): New variable.
	* cppdefault.h (cpp_PREFIX): Document.
	(cpp_PREFIX_len): Likewise.
	(cpp_EXEC_PREFIX): New variable.
	* Makefile.in (PREPROCESSOR_DEFINES): Add STANDARD_EXEC_PREFIX.
	* c-incpath.c (add_standard_paths): Correct logic for relocating
	paths within prefix.

From-SVN: r122843