Facelift MSPDEBUG_TILIB_PATH handling

[melak]

Yes, I primarily just want to get rid of strcat (which is checked and appears to be OK, but still, it's 2018).

Also bring behaviour in line with manual and common expectations:

• In absence of MSPDEBUG_TILIB_PATH, the dynamic linker search path is processed
• If MSPDEBUG_TILIB_PATH is specified, that directory is searched
• The original behaviour in case of an error is graceful fall-through to letting the dynamic linker do its deed
• The behaviour is changed such that if MSPDEBUG_TILIB_PATH is specified, only that path is being considered.

This is in line with both manual and common sense (otherwise one could have just used LD_LIBRARY_PATH).

Poke @DanielO

[DanielO]

Looks good to me, although IMO strcat is fine because it's length checked, I don't really see the snprintf adding any benefit except to satisfy a naive code check.

Note that originally I used asprintf because life is too short but it was rejected because of a concern some platforms might lack it.

[melak]

Yep, no argument about strcat being fine in this particular instance. What I'm after is making the "it's fine" bit more obvious, which is rarely possible with non-bounds-checked string functions, so.

[DanielO]

Fair enough, like I said - looks like it should work to me.

[dlbeer]

Ok, looks good -- thanks.