Fold __builtin_str{n}{case}cmp functions

Fold __builtin_str{n}{case}cmp functions

	* builtins.c (fold_builtin_strcmp): Remove function.
	(fold_builtin_strncmp): Likewise.
	(fold_builtin_2): Remove call of the function.
	(fold_builtin_3): Likewise.
	* fold-const-call.c (fold_const_call): Add constant folding
	for CFN_BUILT_IN_STRCASECMP and CFN_BUILT_IN_STRNCASECMP.
	* fold-const-call.h (build_cmp_result): Declare the function.
	* gimple-fold.c (gimple_load_first_char): New function.
	(gimple_fold_builtin_string_compare): Likewise.
	(gimple_fold_builtin): Call the function.

From-SVN: r241159