Make fallback from P10 to P9 conditional on suitable compiler

driver/others/dynamic_power.c

@@ -53,8 +53,10 @@ static gotoblas_t *get_coretype(void) {
 		return &gotoblas_POWER10;
 #endif
 	/* Fall back to the POWER9 implementation if the toolchain is too old or the MMA feature is not set */
+#if (!defined __GNUC__) || ( __GNUC__ >= 6)
 	if (__builtin_cpu_is("power10"))
 		return &gotoblas_POWER9;
+#endif	
 	return NULL;
 }