Add ability to build SDK libs with Bionic

Add a bionic toolchain target to various support libraries in the NaCl SDK.  Also updates tool scripts such as nacl_gcc.mk to support bionic builds.

These changes require ENABLE_BIONIC=1 and should only affect the experimental bionic build of the NaCl SDK and not Chrome.

BUG=345338
R=binji@chromium.org, sbc@chromium.org

Review URL: https://codereview.chromium.org/171423017

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@253244 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 253244