Use CMake variables instead of as

cmake/system.cmake

@@ -106,10 +106,16 @@ if (CMAKE_C_COMPILER STREQUAL loongcc)
 endif ()
 
 if (POWER)
-  set (NO_WARMUP 1)
-  execute_process(COMMAND bash -c "as -v < /dev/null 2>&1 | grep GNU 2>&1 >/dev/null" RESULT_VARIABLE HAVE_GAS)
-  set(GETARCH_FLAGS	"${GETARCH_FLAGS} -DHAVE_GAS=${HAVE_GAS}")
-endif()
+  set(NO_WARMUP 1)
+  set(HAVE_GAS 1)
+  if (CMAKE_ASM_COMPILER_ID STREQUAL "GNU")
+    set(HAVE_GAS 0)
+  elseif (CMAKE_ASM_COMPILER_ID STREQUAL "Clang")
+    set(CCOMMON_OPT "${CCOMMON_OPT} -fno-integrated-as")
+    set(HAVE_GAS 0)
+  endif ()
+  set(GETARCH_FLAGS "${GETARCH_FLAGS} -DHAVE_GAS=${HAVE_GAS}")
+endif ()
 
 #if don't use Fortran, it will only compile CBLAS.
 if (ONLY_CBLAS)