Fix undefined warning messages in GCC 6.

    GCC 6 puts out warnings in a different location then GCC 5.  Move the
    DIAG macros so that the warnings are supressed for both compilers.

    ChangeLog:

	* soft-fp/fmasf4.c: Add include of sys/cdefs.h.
	Move DIAG_PUSH_NEEDS_COMMENT, DIAG_IGNORE_NEEDS_COMMENT to front of
	file, move DIAG_POP_NEEDS_COMMENT to end of file.
	* soft-fp/fmadf4.c: Ditto.
	* soft-fp/fmatf4.c: Ditto.