Before you bust your Slack install - ask yourself why you want to upgrade GCC.
You can, theoretically, ./configure && make && make install a new GCC. It will probably work.
It is, however, not advisable.
GCC, glibC, binutils and the kernel headers (not the kernel source) are all intertwined in your system and are collective known as "the toolchain". Frequently when upgrading one of those components, it will cease to function and require you up to upgrade another one first, but of course, it's a circular dependancy that will result in you having to "bootstrap" GCC to build the rest.
There's no reason why you can't have more than one compiler on your system (although you'll have to learn how to use a different compiler, and not just ./configure && make && make install) and I would recommend looking into something called "crosstool" to do this. I'm positive you can have multiple compilers (I'm sorry for botching, Kai!) with the same glibc, binutils and kernel headers, but off the top of my head I couldn't say how, and I suspect it's not safe to do so.
The crosstool build matrix is here:
http://kegel.com/crosstool/crosstool-0.37/buildlogs/
And the crosstool main page is here:
http://kegel.com/crosstool/
Detailed reading of the crosstool source will give you a starting point for upgrading your toolchain (since binutils and glibc are better off built by the same GCC you are using ... ), but ultimately you should probably learn how the toolchain is put together so you don't break it.
Back to the original question, though: why do you want to upgrade GCC?
Because it's got a higher version number? Because it's "better" than the one you got with Slack? Because you want to learn how the toolchain works?
I don't think there's a wrong reason for wanting to upgrade, but I wanted you to be aware of the amount of issues you may cause by doing so. Messing with GCC is more sensible than messing with glibC, but do your homework first!
Good luck,
- Piete.
PS: The .SlackBuild script is what is used to make the original Slackware packages. In short it takes the raw tar.bz2 and builds the gcc*.tgz files from source. You will have to modify the SlackBuild script to make it work with the newer GCC and possibly even patch the GCC sources (this is unlikely for an x86 architecture).
PPS: Prerequisites are required. You cannot avoid them. You likely have most of them installed anyway since you have a full toolchain already. GCC can compile itself with only a bare minimal host toolchain in certain circumstances.
PPPS: LFS (linuxfromscratch) is your friend.
