Use AR rcs flags for PNaCl target to avoid warning
Use AR rcs flags for PNaCl target to avoid warning

rwl/blis,rwl/blis,xianyi/blis,arm-hpc/blis,scibuilder/blis,arm-hpc/blis,scibuilder/blis,xianyi/blis,rwl/blis,rwl/blis,xianyi/blis,arm-hpc/blis,xianyi/blis,scibuilder/blis,scibuilder/blis,arm-hpc/blis