RISC-V/testsuite: Add RTL cset-sext.c testcase variants

RISC-V/testsuite: Add RTL cset-sext.c testcase variants

Add RTL tests, for RV64 and RV32 where appropriate, corresponding to the
existing cset-sext.c tests.  They have been produced from RTL code as at
the entry of the "ce1" pass for the respective cset-sext.c tests built
at -O3.

	gcc/testsuite/
	* gcc.target/riscv/cset-sext-rtl.c: New file.
	* gcc.target/riscv/cset-sext-rtl32.c: New file.
	* gcc.target/riscv/cset-sext-sfb-rtl.c: New file.
	* gcc.target/riscv/cset-sext-sfb-rtl32.c: New file.
	* gcc.target/riscv/cset-sext-thead-rtl.c: New file.
	* gcc.target/riscv/cset-sext-ventana-rtl.c: New file.
	* gcc.target/riscv/cset-sext-zicond-rtl.c: New file.
	* gcc.target/riscv/cset-sext-zicond-rtl32.c: New file.