Fix detection of shared library support.
Fix detection of shared library support.

We were previously checking for '--enable-shared' in the
output of 'gcc -version', which turned out to be wrong.
Switching to using 'gcc -print-file-name=libc.so'.

BUG= https://code.google.com/p/nativeclient/issues/detail?id=3834
R=mcgrathr@chromium.org

Review URL: https://codereview.chromium.org/298413002

git-svn-id: 84b3587ce119b778414dcb50e18b7479aacf4f1d@1295 7dad1e8b-422e-d2af-fbf5-8013b78bd812

kuscsik/naclports,Schibum/naclports,kuscsik/naclports,dtkav/naclports,dtkav/naclports,yeyus/naclports,Schibum/naclports,dtkav/naclports,Schibum/naclports,Schibum/naclports,Schibum/naclports,dtkav/naclports,kuscsik/naclports,kuscsik/naclports,yeyus/naclports,yeyus/naclports,dtkav/naclports,yeyus/naclports,kuscsik/naclports,yeyus/naclports,Schibum/naclports,yeyus/naclports