Removing exceptions support from Abseil in Chromium.

If Abseil is compiled with -fexceptions ABSL_HAVE_EXCEPTIONS will be
defined and Abseil will be able to throw. Since exceptions are
forbidden in Chromium's code, this CL removes the possibility to
enable them.

Abseil automatically sets ABSL_HAVE_EXCEPTIONS here:
https://cs.chromium.org/chromium/src/third_party/abseil-cpp/absl/base/config.h?l=207&rcl=f4f0f0e2af28098ac58f8548b13d1a1f46d7c846

Bug: webrtc:8821
Change-Id: I82e19abbe62f332173d977b5ea93f9040232572b
Reviewed-on: https://chromium-review.googlesource.com/1012074Reviewed-by: Nico Weber <thakis@chromium.org>
Commit-Queue: Mirko Bonadei <mbonadei@chromium.org>
Cr-Commit-Position: refs/heads/master@{#550614}

third_party/abseil-cpp/BUILD.gn

@@ -179,18 +179,3 @@ config("absl_test_cflags_cc") {
     }
   }
 }
-
-config("absl_exceptions_cflags_cc") {
-  # Enable exception handling.
-  if (is_win) {
-    cflags_cc = [
-      "/U_HAS_EXCEPTIONS",
-      "/D_HAS_EXCEPTIONS=1",
-      "/EHsc"
-    ]
-  } else {
-    cflags_cc = [
-      "-fexceptions",
-    ]
-  }
-}

third_party/abseil-cpp/absl/base/BUILD.gn

@@ -170,7 +170,6 @@ source_set("base") {
 source_set("throw_delegate") {
   configs += [
     "//third_party/abseil-cpp:absl_default_cflags_cc",
-    "//third_party/abseil-cpp:absl_exceptions_cflags_cc",
   ]
   public_configs = [ "//third_party/abseil-cpp:absl_include_config" ]
   sources = [
@@ -215,7 +214,6 @@ source_set("exception_safety_testing") {
   testonly = true
   configs += [
     "//third_party/abseil-cpp:absl_test_cflags_cc",
-    "//third_party/abseil-cpp:absl_exceptions_cflags_cc",
   ]
 
   public_configs = [ "//third_party/abseil-cpp:absl_include_config" ]

third_party/abseil-cpp/absl/types/BUILD.gn

@@ -18,7 +18,6 @@ if (build_with_chromium) {
 source_set("any") {
   configs += [
     "//third_party/abseil-cpp:absl_default_cflags_cc",
-    "//third_party/abseil-cpp:absl_exceptions_cflags_cc",
   ]
   public_configs = [ "//third_party/abseil-cpp:absl_include_config" ]
   public = [
@@ -36,7 +35,6 @@ source_set("any") {
 source_set("bad_any_cast") {
   configs += [
     "//third_party/abseil-cpp:absl_default_cflags_cc",
-    "//third_party/abseil-cpp:absl_exceptions_cflags_cc",
   ]
   public_configs = [ "//third_party/abseil-cpp:absl_include_config" ]
   sources = [
@@ -86,7 +84,6 @@ source_set("optional") {
 source_set("bad_optional_access") {
   configs += [
     "//third_party/abseil-cpp:absl_default_cflags_cc",
-    "//third_party/abseil-cpp:absl_exceptions_cflags_cc",
   ]
   public_configs = [ "//third_party/abseil-cpp:absl_include_config" ]
   sources = [