cap frequency in make_forwarder_block

cap frequency in make_forwarder_block

In the testcase the block with problematic frequency has to incoming
edges.  Each edge has probability 1.  The first edge's source bb has
frequency 873/10000, and the second has a frequency of 9409/10000.  So
at least one of those is slightly high probably from some sort of rounding
issue related to fixed point, but in any case make_forwarder_block
should not create basic blocks with frequency greater than BB_FREQ_MAX.

gcc/

	PR tree-optimization/64326
	* cfghooks.c (make_forwarder_block): Cap frequency of created
	basic block.

From-SVN: r220585