RISC-V: Leverage stdint-gcc.h for RVV test cases

RISC-V: Leverage stdint-gcc.h for RVV test cases

Leverage stdint-gcc.h for the int64_t types instead of typedef.
Or we may have conflict with stdint-gcc.h in somewhere else.

gcc/testsuite/ChangeLog:

	* gcc.target/riscv/rvv/autovec/unop/math-llrint-0.c: Include
	stdint-gcc.h for int types.
	* gcc.target/riscv/rvv/autovec/unop/math-llrint-run-0.c: Ditto.
	* gcc.target/riscv/rvv/autovec/unop/test-math.h: Remove int64_t
	typedef.

Signed-off-by: Pan Li <pan2.li@intel.com>