[PATCH v3] RISC-V: Add split pattern to generate SFB instructions. [PR113095]

[PATCH v3] RISC-V: Add split pattern to generate SFB instructions. [PR113095]

Since the match.pd transforms (zero_one == 0) ? y : z <op> y,
into ((typeof(y))zero_one * z) <op> y. Add splitters to recongize
this expression to generate SFB instructions.

gcc/ChangeLog:
	PR target/113095
	* config/riscv/riscv.md: New splitters to rewrite single bit
	sign extension as the condition to SFB instructions.

gcc/testsuite/ChangeLog:
	* gcc.target/riscv/sfb.c: New test.
	* gcc.target/riscv/pr113095.c: New test.

(cherry picked from commit fb54b9772816968032518d4008be5090e0d95109)