Verify, for generic floating-point conditional-add operations that have
a corresponding conditional-set machine instruction, that if-conversion
does *not* trigger at `-mbranch-cost=2' setting, which makes original
branched code sequences cheaper than their branchless equivalents
if-conversion would emit.  Cover all the relevant floating-point
relational operations to make sure no corner case escapes.

	gcc/testsuite/
	* gcc.target/riscv/adddibfeq.c: New test.
	* gcc.target/riscv/adddibfge.c: New test.
	* gcc.target/riscv/adddibfgt.c: New test.
	* gcc.target/riscv/adddibfle.c: New test.
	* gcc.target/riscv/adddibflt.c: New test.
	* gcc.target/riscv/addsibfeq.c: New test.
	* gcc.target/riscv/addsibfge.c: New test.
	* gcc.target/riscv/addsibfgt.c: New test.
	* gcc.target/riscv/addsibfle.c: New test.
	* gcc.target/riscv/addsibflt.c: New test.