Enable -Wexit-time-destructors and -Wglobal-constructors.

This CL enables -Wexit-time-destructors and -Wglobal-constructors on
rtc_static_library and rtc_source_set build targets.

It also adds the possibility to suppress these warnings because
they trigger in a few places.

The long term goal is to avoid regressions on this and remove all the
suppressions.

Bug: webrtc:9693
Change-Id: I4c1ecc137ef9e87ec5e66981ce95d96fb082727c
Reviewed-on: https://webrtc-review.googlesource.com/98380
Reviewed-by: Karl Wiberg <kwiberg@webrtc.org>
Commit-Queue: Mirko Bonadei <mbonadei@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#24604}

pc/BUILD.gn

@@ -117,6 +117,7 @@ rtc_source_set("rtc_pc") {
 rtc_static_library("peerconnection") {
   visibility = [ "*" ]
   cflags = []
+  configs += [ "..:no_exit_time_destructors" ]
   sources = [
     "audiotrack.cc",
     "audiotrack.h",