PR driver/67613 - spell suggestions for misspelled command line options

PR driver/67613 - spell suggestions for misspelled command line options

gcc/ChangeLog:
	PR driver/67613
	* Makefile.in (GCC_OBJS): Add spellcheck.o.
	(OBJS): Add spellcheck-tree.o.
	* gcc.c: Include "spellcheck.h".
	(suggest_option): New function.
	(driver::handle_unrecognized_options): Call suggest_option to
	provide a hint about misspelled options.
	* spellcheck.c: Update file comment.
	(levenshtein_distance): Convert 4-param implementation from static
	to extern scope.  Remove note about unit tests from leading
	comment for const char * implementation.  Move tree
	implementation to...
	* spellcheck-tree.c: New file.
	* spellcheck.h (levenshtein_distance):  Add 4-param decl.

gcc/testsuite/ChangeLog:
	PR driver/67613
	* gcc/testsuite/gcc.dg/spellcheck-options-1.c: New file.
	* gcc/testsuite/gcc.dg/spellcheck-options-2.c: New file.

From-SVN: r230285