build/make/iosbuild.sh: Be more explicit about armv7.

xcode defines __ARM_ARCH_7A__ for armv7, not __ARM_ARCH_7__.

Change-Id: I0184e253a856e74c133d987ec6f6990f0923bb29

build/make/iosbuild.sh

@@ -62,7 +62,7 @@ target_to_preproc_symbol() {
       echo "__ARM_ARCH_6__"
       ;;
     armv7-*)
-      echo "__ARM_ARCH_7__"
+      echo "__ARM_ARCH_7A__"
       ;;
     armv7s-*)
       echo "__ARM_ARCH_7S__"