Compile libjingle for PNaCl

Added libjingle_nacl target that compile libjingle for PNaCl.
Removed dependency on jsoncpp.

BUG=276739

Review URL: https://codereview.chromium.org/173013003

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@252825 0039d316-1c4b-4281-b951-d872f2087c98
PNaCl documentation: add undefined behavior

The text was sent to the LLVM mailing list, I edited it a bit and restified it. See:
http://lists.cs.uiuc.edu/pipermail/llvmdev/2013-June/063010.html

R= binji@chromium.org, sbc@chromium.org, dschuff@chromium.org, mseaborn@chromium.org, jvoung@chromium.org, stichnot@chromium.org, sehr@chromium.org, ncbray@chromium.org, mackinlay@chromium.org
TEST= none
BUG= none
NOTRY=true
(documentation only change)

Review URL: https://codereview.chromium.org/164413005

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@252826 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 252825
SVN changes up to revision 252826