RISC-V/testsuite: Add branched cases for generic integer cond adds

Verify, for generic integer conditional-add operations, if-conversion
*not* to trigger at the respective sufficiently low `-mbranch-cost='
settings that make original branched code sequences cheaper than their
branchless equivalents if-conversion would emit.  Cover all integer
relational operations to make sure no corner case escapes.

	gcc/testsuite/
	* gcc.target/riscv/adddibeq.c: New test.
	* gcc.target/riscv/adddibge.c: New test.
	* gcc.target/riscv/adddibgeu.c: New test.
	* gcc.target/riscv/adddibgt.c: New test.
	* gcc.target/riscv/adddibgtu.c: New test.
	* gcc.target/riscv/adddible.c: New test.
	* gcc.target/riscv/adddibleu.c: New test.
	* gcc.target/riscv/adddiblt.c: New test.
	* gcc.target/riscv/adddibltu.c: New test.
	* gcc.target/riscv/adddibne.c: New test.
	* gcc.target/riscv/addsibeq.c: New test.
	* gcc.target/riscv/addsibge.c: New test.
	* gcc.target/riscv/addsibgeu.c: New test.
	* gcc.target/riscv/addsibgt.c: New test.
	* gcc.target/riscv/addsibgtu.c: New test.
	* gcc.target/riscv/addsible.c: New test.
	* gcc.target/riscv/addsibleu.c: New test.
	* gcc.target/riscv/addsiblt.c: New test.
	* gcc.target/riscv/addsibltu.c: New test.
	* gcc.target/riscv/addsibne.c: New test.