MVSGCC
This is a port of the GCC compiler suite to IBM MVS, a predecessor of modern z/OS.
It has been repackaged here for easier collaboration.
Building
On most UNIX environments all you need to do is 'make'. At the moment this will build cross-compilers for MVS, CMS and VSE. Read the makefile for other options.
My new make-based build system does not support building a C library yet. You would normally use something called PDPCLIB for that.