RISC-V: Fix reduc_strict_run-1 test case.

RISC-V: Fix reduc_strict_run-1 test case.

This patch fixes the reduc_strict_run-1 testcase by introducing
a variable that holds the reference result.  This is necessary
because in presence of _Float16 emulation an intermediate
result used in a comparison is computed in higher precision.

gcc/testsuite/ChangeLog:

	* gcc.target/riscv/rvv/autovec/reduc/reduc_strict_run-1.c:
	Add variable to hold reference result.