Recover behaviour of only setting SIMD_FLAGS to most specific value, rather...

Recover behaviour of only setting SIMD_FLAGS to most specific value, rather than all accepted values. Save intel compiler warnings about ignoring flags.

m4/ax_ext.m4

@@ -43,6 +43,10 @@
 #   and this notice are preserved. This file is offered as-is, without any
 #   warranty.
 
+#   SWIFT modifications. Intel compilers accept these flags, but warn about
+#   the order of the flags when more than one is used. Given that we just
+#   set SIMD_FLAGS to the most specific value, rather than all accepted ones.
+
 #serial 15
 
 AC_DEFUN([AX_EXT],
@@ -248,7 +252,7 @@ AC_DEFUN([AX_EXT],
              AX_CHECK_COMPILE_FLAG(${ac_instr_compiler_flags}, eval ax_cv_support_${ac_instr_acvar}_ext=yes,
                                                                eval ax_cv_support_${ac_instr_acvar}_ext=no)
              if test x"$(eval echo \$ax_cv_support_${ac_instr_acvar}_ext)" = x"yes"; then
-               eval ${ac_instr_flag_type}=\"\$${ac_instr_flag_type} ${ac_instr_compiler_flags}\"
+               eval ${ac_instr_flag_type}=\"${ac_instr_compiler_flags}\"
                AC_DEFINE_UNQUOTED([${ac_instr_have_define}])
              else
                AC_MSG_WARN([Your processor and OS supports ${ac_instr_shortname} instructions but not your compiler, can you try another compiler?])