Roll Clang from 026df9514ead to ca6196138012.

Fix new -Werror=unused-command-line-argument for -stdlib=libc++.

Change-Id: I7e6056323b7bb6da49b80299380be6ed7b70c582
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/278691
Reviewed-by: Siva Annamalai <asiva@google.com>
Commit-Queue: Ryan Macnak <rmacnak@google.com>

DEPS

@@ -74,7 +74,7 @@ vars = {
   # The list of revisions for these tools comes from Fuchsia, here:
   # https://fuchsia.googlesource.com/integration/+/HEAD/toolchain
   # If there are problems with the toolchain, contact fuchsia-toolchain@.
-  "clang_version": "git_revision:026df9514eada25e72ff69a587a580fd29ff2732",
+  "clang_version": "git_revision:ca619613801233ef2def8c3cc7d311d5ed0033cb",
   "gn_version": "git_revision:0bcd37bd2b83f1a9ee17088037ebdfe6eab6d31a",
 
   # Update from https://chrome-infra-packages.appspot.com/p/fuchsia/sdk/gn

build/config/mac/BUILD.gn

@@ -6,13 +6,10 @@ import("//build/config/sysroot.gni")
 import("../clang/clang.gni")
 
 config("sdk") {
-  common_flags = [ "-stdlib=libc++" ]
-
-  cflags = common_flags
-  ldflags = common_flags + [
-              "-nostdlib++",
-              "${clang_prefix}/../lib/libc++.a",
-            ]
+  ldflags = [
+    "-nostdlib++",
+    "${clang_prefix}/../lib/libc++.a",
+  ]
 }
 
 # On Mac, this is used for everything except static libraries.