ios: Pass -Wextra-semi to ObjC files with Xcode clang too.

https://reviews.llvm.org/rL356148 landed 1.5 years ago, it's hopefully
available in Xcode now. Also, we no longer support use_system_xcode
builds in chromium/ios.

Bug: 926235
Change-Id: I50e77e1b4c2e7419ab6be40fc00eb62b44548c24
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2510190
Auto-Submit: Nico Weber <thakis@chromium.org>
Reviewed-by: Hans Wennborg <hans@chromium.org>
Commit-Queue: Nico Weber <thakis@chromium.org>
Cr-Commit-Position: refs/heads/master@{#822659}

build/config/compiler/BUILD.gn

@@ -1662,11 +1662,7 @@ config("chromium_code") {
     # ChromeOS: http://crbug.com/940863
     # Chromecast: http://crbug.com/942554
     has_dchecks = is_debug || dcheck_always_on
-    if (!has_dchecks && is_ios && use_xcode_clang) {
-      # TODO(thakis): Remove this branch once Xcode's clang has clang r356148.
-      cflags_c = [ "-Wextra-semi" ]
-      cflags_cc = [ "-Wextra-semi" ]
-    } else if (!has_dchecks && is_chromeos && is_chrome_branded) {
+    if (!has_dchecks && is_chromeos && is_chrome_branded) {
       # Temporarily disable -Wextra-semi for Chrome on Chrome OS.
     } else if (is_chromecast && chromecast_branding != "public") {
       # Temporarily disable -Wextra-semi for Chromecast.