I did some work on updating gpc to newer gcc versions. You can find it at GitHub:
https://github.com/hebisch/gpc
This is experimental work. 4.2 and 4.3 ports (on "master" Git branch) are basically in "works for my purpose" state: on my machine compiler builds and passes test suite with small (but nonzero) number of failures. On 4.5.1 there is initial port to gcc-4.[45] -- this one is broken from user point of view and may be of some use only for people who want to seriously work on the compiler.
Note that this is _not_ a release. There are relatively easy to fix but non working things (in particular some features of Makefiles are broken). Testing was limited to running testsute just for one configuration. I estimate that fixing easily fixable stuff and polishing things would take me about a week -- unfortunately I am busy with other things. So I decided to make the code available "as is". If there will be bug reports, I will look at them and there is reasonable chance that I will fix them. But otherwise I do not plan to work on gpc in near future.
If you want to try the code note that there are changes to build process, look at toplevel README file.