SERVER-13544 Enable gperftools for C++11 builds

The following change was backported:
https://code.google.com/p/gperftools/source/detail?r=18fbc316eebea9db2d7ec41e161c0a3fbb09fa42

Another change we wanted was:
https://code.google.com/p/gperftools/source/detail?r=6287bbbbad8730712cfd1ee28ecc0648cbaa9f94#

However, since that patch must hit every PR/SC instance and the code has evolved from that point
we instead just ran the following two scripts over the gperftools source tree:

find . -type f | xargs egrep -l '"PR\w+"' | xargs perl -pi -e 's|"PR(\w+)"|" PR\1 "|g'
find . -type f | xargs egrep -l '"SC\w+"' | xargs perl -pi -e 's|"SC(\w+)"|" SC\1 "|g'

and then manually fixing up the one reference to GPRIuPTHREAD, which achieved the same result.

Finally, remove the logic preventing mixture of C++11 and gperftools from the build system.