Fix CMake warning

Summary: Latest CMake on OS X with brew surfaced this warning and that
this check was not doing what it was originally intended to do.
Fix three eval() bugs

* @ eval() was not being silenced correctly
* If the string passed to eval() hits a parse error, then the runtime
  is not supposed to fatal. We currently do.
* Errors in eval() code did not print a valid file name, they now
  print it as "$FILENAME($LINE1) : eval()'d code on line $LINE2"

Closes #945

Reviewed By: @jdelong

Differential Revision: D1006603
Fixes for PGO mode

This fixes a couple of asserts I hit running www in DEBUG mode with
-vEval.JitPGO=1 -vEval.JitRegionSelector=hottrace
-vEval.JitPGOHotOnly=0.

Reviewed By: @ottoni

Differential Revision: D1016284