Fixed undefined symbols PRIu64/PRIu32 and reference to clock_gettime

[francoisbertelatschrodinger]

On CentOS6.8 with a local build of g++ 6.4.0 (the default g++ version on CentOS6.8 is 4.4.7), the build fails with undefined symbol PRIu64 and PRIu32 at compile time and undefined reference to 'clock_gettime' at link time.

Fixed undefined symbols PRIu64/PRIu32 by including <cinttypes> instead of
<inttypes.h>. (a less elegant solution would be to add #define __STDC_FORMAT_MACROS prior to include <inttypes.h>). layersvt/device_simulation.cpp is a C++ file and as such should include C header files that way anyway (note that this file includes other C header files the wrong way: <stdarg.h>, <stdio.h>, <stdlib.h> and <string.h> instead of <cstdarg>, <cstdio>, <cstdlib> and <cstring> respectively. I have not fixed these inclusions in the current patch as I want to keep it minimal to address the actual build issue)

Fixed undefined reference to clock_gettime by linking rt library
This fix is similar to KhronosGroup/SPIRV-Tools#2409

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[francoisbertelatschrodinger]

In case you have not been notified automatically, I signed the CLA on Feb 28 2019.