RISC-V: Fix simplify_ior_optimization.c on rv32

GCC will complaint if target ABI isn't have corresponding multi-lib on
glibc toolchain, use stdint-gcc.h to suppress that.

gcc/testsuite/ChangeLog:

	* gcc.target/riscv/simplify_ior_optimization.c: Use stdint-gcc.h
	rather than stdint.h