[Ohrrpgce] SVN: teeemcee/12265 On Linux, print backtraces also on FB errors, and improve error messages

[subversion at HamsterRepublic.com]

teeemcee
2021-04-15 21:55:52 -0700 (Thu, 15 Apr 2021)
529
On Linux, print backtraces also on FB errors, and improve error messages

As well as printing the backtrace also decode the signal number to a name, and
print the module and function names in debugging builds, like it did before
r12249.

Also catch a few more signals.

Also change shift-tab-F6 to a null ptr access test.

And try to avoid a gfx_close() deadlock when quitting from a fatal error

Also, if DrMingw is in use (which is never, except when I test it) also log
backtraces on Windows when showerror_internal is called.
---
U   wip/allmodex.bas
U   wip/common.rbas
U   wip/common_base.bi
U   wip/misc.h
U   wip/os.bi
U   wip/os.h
U   wip/os_unix.c
U   wip/os_windows.bas