Don't assert "alg != libcall" for -minline-stringops-dynamically

Backported from mainline:

gcc/

	PR target/64200
	* config/i386/i386.c (decide_alg): Don't assert "alg != libcall"
	for TARGET_INLINE_STRINGOPS_DYNAMICALLY.

gcc/testsuite/

	PR target/64200
	* gcc.target/i386/memcpy-strategy-4.c: New test.


git-svn-id: svn+ssh://gcc.gnu.org/svn/gcc/branches/gcc-4_9-branch@218718 138bc75d-0d04-0410-961f-82ee72b054a4