Add USE_MALLOC define, to toggle the use of malloc() and free() instead of VLA

[davidebeatrici]

This is required for MSVC.

[petterreinholdtsen]

The USE_MALLOC name is a bit confusing, as the code of course use mallom even if USE_MALLOC is not defined... What about HAVE_VLA_SUPPORT or something like that instead? Is there some flag in modern C that can be used to detect compilers with such advanced feature available without manually setting a flag?

[davidebeatrici]

According to https://stackoverflow.com/a/49988810 we can use __STDC_NO_VLA__.

[davidebeatrici]

Should I do that?

[petterreinholdtsen]

[Davide Beatrici]

Should I do that?

I have no idea who would make such decision, but for what it is worth, I believe it is a better idea to automatically detect the need than to depend on a manually set flag. So if it was up to me, I would do it. :) -- Happy hacking Petter Reinholdtsen

[marler8997]

Here's my own take on a fix: #219

Relevant differences:

• use alloca instead of malloc
• use C std version and __STDC_NO_VLA__ to automatically determine VLA support
  • application still has the option to manually define NO_VLA if the automatic detection doesn't work with their toolchain
• define a stackalloc abstraction so we don't need the ifdefs all over the source

[jmvalin]

Can you give the upgrade1 branch a try. The VLAs should all be replaced with fixes sizes.