add warning flags by default

configure.ac

@@ -52,6 +52,11 @@ AC_TYPE_UINT64_T
 AC_TYPE_SIZE_T
 AC_TYPE_SSIZE_T
 
+# Add warning flags by default
+AX_CHECK_COMPILE_FLAG([-Wall], [CFLAGS="$CFLAGS -Wall"])
+AX_CHECK_COMPILE_FLAG([-Wextra], [CFLAGS="$CFLAGS -Wextra"])
+AX_CHECK_COMPILE_FLAG([-Wshadow], [CFLAGS="$CFLAGS -Wshadow"])
+
 # Checks for library functions.
 AC_CHECK_FUNCS([memset])
 AC_CHECK_LIB([pthread],[pthread_create],,[AC_MSG_ERROR([Could not find pthread_create!])])