* builtins.c (expand_builtin_strncmp, expand_builtin_strncpy): New
	functions.
	(expand_builtin): Handle BUILT_IN_STRNCPY and BUILT_IN_STRNCMP.

	* builtins.def (BUILT_IN_STRNCPY, BUILT_IN_STRNCMP): New entries.

	* c-common.c (c_common_nodes_and_builtins): Declare builtin
	strncpy and strncmp.

	* extend.texi (strncmp, strncpy): Document new builtins.

testsuite:
	* gcc.c-torture/execute/string-opt-7.c: New test.
	* gcc.c-torture/execute/string-opt-8.c: Likewise.

From-SVN: r37777