The two tests use decimal floating point, add the relevant dg-requires
so that they are unsupported on platforms without DFP.

2019-06-22  Iain Sandoe  <iain@sandoe.co.uk>

	* gcc.target/powerpc/pr64205.c: Require effective target dfp.
	* gcc.target/powerpc/pr79909.c: Likewise.

From-SVN: r272592