Update READMEs

BUG=none
R=sky@chromium.org

Review URL: https://codereview.chromium.org/25091003

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@225792 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 225792
[NaCl SDK] Remove pnacl.h from the sdk.

The __builtin_nacl_target_arch that it defines is not
part of the PNaCl bitcode ABI.  For non-pnacl cases, it has
#error when !defined(__pnacl__) so doesn't make sense to
have there either.

It is only used in the private build of pnacl-llc.

BUG=https://code.google.com/p/nativeclient/issues/detail?id=3525
NOTRY=true

Review URL: https://codereview.chromium.org/25039005

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@225793 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 225793