[gcc] Add nacl to libstdc++'s list of glibc-based architectures

Note that this does not affect newlib-based libstdc++ builds, for
which crossconfig.m4 is not consulted (see configure.ac).

Update "configure" by running autoconf 2.59.

BUG=http://code.google.com/p/nativeclient/issues/detail?id=660
TEST=build full-gcc against nacl-glibc

Review URL: http://codereview.chromium.org/3181032