Fixing clang-cl 'unknown argument error'.

Bug: webrtc:8821
Change-Id: I491118ef06695897f001a27ccd296501cf6b72d7
Reviewed-on: https://chromium-review.googlesource.com/1011608Reviewed-by: Patrik Höglund <phoglund@chromium.org>
Commit-Queue: Mirko Bonadei <mbonadei@chromium.org>
Cr-Commit-Position: refs/heads/master@{#550552}

third_party/abseil-cpp/BUILD.gn

@@ -151,6 +151,10 @@ config("absl_test_cflags_cc") {
 
 config("absl_exceptions_cflags_cc") {
   cflags_cc = [
-    "-fexceptions",
+    # Enable exception handling.
+    # It seems clang-cl does not support -fexception. Using the MSVC flag
+    # fixes the problem.
+    # "-fexceptions",
+    "/GX",
   ]
 }