Make Config::default_value leak instead of having an exit-time destructor.
Make Config::default_value leak instead of having an exit-time destructor.

I wanted to use Config::Get in Chromium code, but it triggered the following
warning:
../../third_party/webrtc/common.h:89:20: error: declaration requires an exit-time destructor [-Werror,-Wexit-time-destructors]
    static const T def;
                   ^
../../third_party/webrtc/common.h:110:10: note: in instantiation of function template specialization requested here
  return default_value<T>();
         ^

I assume we don't hit this in webrtc because the warning is disabled.

This also switches to the RTC_ prefix from the deprecated LIBJINGLE_.

Needed due to this Chromium CL:
https://codereview.chromium.org/1148843004/

R=andresp@webrtc.org, tommi@webrtc.org

Review URL: https://webrtc-codereview.appspot.com/53459004

Cr-Original-Commit-Position: 972c6d2dc6dd5efdad1377c0d224e03eb8f276f7@{#9268}
Cr-Mirrored-From: https://chromium.googlesource.com/external/webrtc
Cr-Mirrored-Commit: 469c2c04aae3e8446ba35f482adabd42800b41e1

dcpang/fatline-libjingle,sippet/talk,dcpang/fatline-libjingle,sippet/talk,dcpang/fatline-libjingle,dcpang/fatline-libjingle,sippet/talk,sippet/talk,dcpang/fatline-libjingle,sippet/talk