* defaults.h (CPLUSPLUS_CPP_SPEC): New macro.
	* gcc.c (struct compiler): Add cpp_spec field.
	(input_file_compiler): New variable.
	(do_spec_1): Allow a particular compiler to handle `%C'
	specially.
	(main): Store the current compiler in input_file_compiler.
	* tm.texi (CPLUSPLUS_CPP_SPEC): Document.

	* lang-specs.h: Use CPLUSPLUS_CPP_SPEC for the preprocessor
	spec.

From-SVN: r39524