install: Removed lib dir assumptions, closes #13810

[iliekturtles]

I see that CFG_LIBDIR and CFG_LIBDIR_RELATIVE are already exported somewhere by the time install.sh is run when doing make install. Why aren't CFG_MANDIR and CFG_MANDIR_RELATIVE exported? I'm guessing that none of these variables can be relied on for binary distribution situations? Is this why line 228 assumes lib if no --libdir option is given?

My solution relies on CFG_PREFIX being the prefix to CFG_LIBDIR and CFG_MANDIR and that the relative portion of the path will match in both the source and destination. Is this a valid assumption?

I tested make install on both mingw32 and Linux. Are there any other targets I should run when making changes to install.sh?

[pnkfelix]

I am not sure this is robust enough, If the invoker of install.sh passes --libdir they may choose a value that does not match your assumptions about the relationships at the source and destinations.

Cc @brson

[iliekturtles]

I think you're right about that. And if CFG_LIBDIR_RELATIVE cannot be relied on as I expect then the script will need new/different parameters in order support mingw32.

[brson]

@iliekturtles Thanks for picking this issue up, and sorry I've been neglecting it. I've left my comments over there.

Per those comments, I think this is indeed not a viable solution though, so closing.