SERVER-13944 Switch back to -fPIC instead of -fPIE to fix RHEL6.2 build.

On RHEL6 builders, the -fPIE compiler flag causes the mongo shell to make
a pure virtual function call inside the V8 engine at startup.  Since
the swtitch to -fPIE was unnecessary for SERVER-13944, switching back to
-fPIC pending investigation.