Verify, for generic floating-point conditional-add operations that have
a corresponding conditional-set machine instruction, that if-conversion
triggers via `noce_try_addcc' at `-mbranch-cost=3' setting, which makes
branchless code sequences emitted by if-conversion cheaper than their
original branched equivalents, and that extraneous instructions such as
SNEZ, etc. are not present in output.

The reason to XFAIL SImode tests for RV64 targets is the compiler thinks
it has to sign-extend addends, which causes if-conversion to give up.

	gcc/testsuite/
	* gcc.target/riscv/adddifeq.c: New test.
	* gcc.target/riscv/adddifge.c: New test.
	* gcc.target/riscv/adddifgt.c: New test.
	* gcc.target/riscv/adddifle.c: New test.
	* gcc.target/riscv/adddiflt.c: New test.
	* gcc.target/riscv/addsifeq.c: New test.
	* gcc.target/riscv/addsifge.c: New test.
	* gcc.target/riscv/addsifgt.c: New test.
	* gcc.target/riscv/addsifle.c: New test.
	* gcc.target/riscv/addsiflt.c: New test.