Prefix flag macros with WEBRTC_.

Macros defined in rtc_base/flags.h are intended to be used to define
flags in WebRTC's binaries (e.g. tests).

They are currently not prefixed and this could cause problems with
downstream clients since these names are quite common.

This CL adds the 'WEBRTC_' prefix to them.

Generated with:

for x in DECLARE DEFINE; do
  for y in bool int float string FLAG; do
    git grep -l "\b$x\_$y\b" | \
    xargs sed -i "s/\b$x\_$y\b/WEBRTC_$x\_$y/g"
  done
done
git cl format

Bug: webrtc:9884
Change-Id: I7b524762b6a3e5aa5b2fc2395edd3e1a0fe72591
Reviewed-on: https://webrtc-review.googlesource.com/c/106682
Reviewed-by: Karl Wiberg <kwiberg@webrtc.org>
Commit-Queue: Mirko Bonadei <mbonadei@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#25270}

modules/audio_coding/neteq/tools/neteq_rtpplay.cc

@@ -17,17 +17,17 @@
 #include "system_wrappers/include/field_trial.h"
 #include "test/field_trial.h"
 
-DEFINE_bool(codec_map,
-            false,
-            "Prints the mapping between RTP payload type and "
-            "codec");
-DEFINE_string(
+WEBRTC_DEFINE_bool(codec_map,
+                   false,
+                   "Prints the mapping between RTP payload type and "
+                   "codec");
+WEBRTC_DEFINE_string(
     force_fieldtrials,
     "",
     "Field trials control experimental feature code which can be forced. "
     "E.g. running with --force_fieldtrials=WebRTC-FooFeature/Enable/"
     " will assign the group Enable to field trial WebRTC-FooFeature.");
-DEFINE_bool(help, false, "Prints this message");
+WEBRTC_DEFINE_bool(help, false, "Prints this message");
 
 int main(int argc, char* argv[]) {
   webrtc::test::NetEqTestFactory factory;