Remove warnings from Intel VTune Amplifier about signal stack being too small

Intel VTune Amplifier XE 2013 requires a 64K signal stack on Linux.  (See page 16 [here](https://software.intel.com/sites/default/files/article/251102/release-notes-amplifier-xe-linux-update4.pdf) for details).  This pull request provides this size stack if all three of the following conditions are true:
* Julia is running on Linux.
* Julia was configured with ```USE_INTEL_JITEVENTS```.
* Julia is running under Intel VTune Amplifier.
Otherwise, the signal stack size is the same.  If Julia is not configured with ```USE_INTEL_JITEVENTS```, no overhead (in space or time) is incurred.