Fix mmap bug in libgit2
Fix mmap bug in libgit2

libgit2 was using mmap with SHARED+WRITABLE to write
to an ofset with a file.  However this is not possible
when NO_MMAP is defined, so in this case just use
pwrite().

This fixes the clone operation for libgit2 on NaCl.

R=binji@chromium.org

Review URL: https://codereview.chromium.org/613293004

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