Why might you want to rebuild JLib? Well, you might want a build with debug info, make some changes, fix the odd bug, want to alter the way errors are handled, or be an emx person.
There are issues to do with C runtime libraries, too.
The makefile included in this distribution is for gnu make 3.74. Get your copy from the usual sites. You'll also need various gnu tools: rm, cp, tee, & cat. And a suitable shell; I use version 2.00 of gnu bash. My executable is called gbash.exe, if yours is different then alter the first line in the makefile.
Don't save the makefile from an editor which converts tabs to spaces.
You'll need a compiler (duh). Visualage & emx are recognised, if you want to use emx then you'll also need the multimedia kit (search for mm4emx11.zip).
Make sure you've unzipped JLIBSRC.ZIP.
Choose the compiler. The default is Visualage; to use emx do SET JLIB_BUILD_MODE=EMX. If you want to use emx, you'll need to edit the file mkres.cmd to point to your emx installation.
Choose the exception model. The default is to use exceptions; to turn them off do SET JLIB_EXCEPTIONS=NO.
Choose the debug level. The default is no debug info; to turn it on, do SET JLIB_DEBUG=YES.
Change directory to X:\JLIB and run the script `m.cmd'. This should run the build and send messages to the screen & a file called `log'.
Using Visualage, everything should go very smoothly.
Using emx, there are a slew of warnings from emxomf (if this is a debug build), and a handful of warnings from gcc.