fightwarn - avoid variable-length arrays, their support became optional after C99

[jimklimov]

Follows up from #823 / #844 efforts, this PR avoids initializing variable-length arrays in the code. In most cases it was changed to dynamic xmalloc/free-before-return handling. A couple of subsequent fixes for rhino.c also got here, which depend on these changes.

In the solis.c driver it was just replaced by the macro which (in header) initializes the unmodifiable (right?) typed variable:

#define PACKET_SIZE 25
static const int packet_size = PACKET_SIZE;

[lgtm-com]

This pull request introduces 1 alert when merging f0167e6 into 1d9d22a - view on LGTM.com

new alerts:

• 1 for FIXME comment

[lgtm-com]

This pull request introduces 1 alert when merging 836a4fb into e3a5544 - view on LGTM.com

new alerts:

• 1 for FIXME comment

[clepple]

Changes seem reasonable, but as with a lot of the other changes, we'll want to mention in the release notes (or better yet, on the lists beforehand) that testing is needed.