Changes to support VS 2017 builds for Win64 bench-marking.

[JakeKirk]

This is my first pull request, bear with me as I learn how this all works.

Here are the change notes:
Changes have been tested on Kubuntu gcc/cc 7.3.0 and VS 2017 (Win64).

• Added cross platform "getopts" parg.c/h to assist with this goal.
• Reworked benchmark_codec_with_options()
  -#ifdef conditionalize fork(), exit() and wait() logic.
  • added FILENAME_MAX for fifo_name size, whether mktemp() or GetTempFileNameA() is used.
• Created append_csv_benchmark() to assist with readabilty and simplify Win32/Linux changes.
• mktemp() on Win32 creates only 26 unique temp files names (which normally are deleted if no errors occur, but can fail if file pre-exists.
  Therefore decided to use GetTempFileNameA() instead which creates a larger set of temporary file names.
• Added a few comments, made a few indentation changes (hope tabs match!), added a few constants.

[JakeKirk]

On Win32...
By default open() without the O_BINARY flag appears to be in "text mode" and if the results intermittently contain a Ctrl-Z value... the read() then fails/stops prematurely (and the results where not written/moved to CSV and were missing, but logs show that the "level" had been completed). So this fixes the intermittent missing "level" results in the CSV. The bytes_read didn't match sizeof(SquashBenchmarkResult), bytes_read was something less and processing was skipped. Error logging of failure to read less than the expected bytes was also added. I also thought about #pragma pack(1) alignment on SquashBenchmarkResult but it doesn't seem to be needed if the O_BINARY flag is used. This also fixes a bad data alignment side-effect. What I saw in the CSV was a structure alignment read/write issue and looked like this (negative #'s, missing data, extremely large values):
MyDataSet1.DZT,brotli,brotli,3,2052096,218762561,-0.000000,-0.000000,-0.000000,-0.000000
MyDataSet1.DZT,brotli,brotli,10,2052096,168680826,-82280922714874703238086033564862959098824282080290866632698245024619752864926095607914748551723551