Fix compile errors on Linux

[jhannemann]

The changes below fix compile errors experienced on Ubuntu 16.04 LTS
with GCC 5.4.0.

• On Linux, <sys/time.h> must be included to make struct timeval known.
• <math.h> does not include std:sqrt. <cmath> does.
• must be included to use fopen().
• string.h must be included to use memset().
• A jump to a label (done_close_file) must not cross local
  declarations. The corresponding code has been encapsulated in a block.
• The use of the STRINGIZE macro leads to an error where the compiler
  sees the #version 430 sequence as an invalid preprocessor directive.
  Removing the # from #version fixes this.

[bsmr]

I almost created a pull request with the same changes. But I checked the pull-requests before submitting it. Well, I should have checked the pull-requests, before working on the patches.

Question

A question about 12-particlesimulator.cpp and the #version problem: removing the # makes it compile, but is this still a valid shader?

I could make it compile with adding a \ to #, e.g. \#version 430 core, but I am not sure, if this compiles to a proper shader. Maybe I will add some error handling code to vglAttachShaderSource(). Besides, I also removed the trailing \n.

But I couldn't test the output, because my current gfx card only supports 410, and this example is one of the few, which I couldn't get working properly. Only 01-triangles gives me some trouble as well, all the other examples do work.

System Information

$ glxinfo | grep -i version
server glx version string: 1.4
client glx version string: 1.4
GLX version: 1.4
    Version: 17.2.2
    Max core profile version: 4.1
    Max compat profile version: 3.0
    Max GLES1 profile version: 1.1
    Max GLES[23] profile version: 3.0
OpenGL core profile version string: 4.1 (Core Profile) Mesa 17.2.2
OpenGL core profile shading language version string: 4.10
OpenGL version string: 3.0 Mesa 17.2.2
OpenGL shading language version string: 1.30
OpenGL ES profile version string: OpenGL ES 3.0 Mesa 17.2.2
OpenGL ES profile shading language version string: OpenGL ES GLSL ES 3.00

$ g++ --version
g++ (Ubuntu 7.2.0-8ubuntu3) 7.2.0
Copyright (C) 2017 Free Software Foundation, Inc.
This is free software; see the source for copying conditions.  There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.

$ uname --all
Linux abyss 4.13.0-16-generic #19-Ubuntu SMP Wed Oct 11 18:35:14 UTC 2017 x86_64 x86_64 x86_64 GNU/Linux

$ lsb_release --all
No LSB modules are available.
Distributor ID:	Ubuntu
Description:	Ubuntu 17.10
Release:	17.10
Codename:	artful

[jhannemann]

Well, looking back, I don't know why I removed the # rather than escaping it. Not sure whether it actually compiles correctly, but IIRC it did. I'll revisit this when teaching my class next semester. Thanks for noticing this.

[johnkslang]

Do you want to resubmit without the change to #, or a change to # that preserves it?