viswa informs us of a source for “Completely Free Open Source GCC builds for ARM MCUs and MPUs. This seems to be maintained by the official team which maintains GCC for ARM. This is useful for ARM Cortex M / Cortex R processors.”
Pre-built GNU toolchains from ARM Cortex-R & Cortex-M processors, together with source code can be found here. (Note that the reference to “launchpad” in the URL refers to the Launchpad open source suite of tools for software collaboration and not the MSP430 Launchpad hardware.)
Via the contact form.
Another pre-built GNU toolchain for ARM processors is
http://sourceforge.net/projects/devkitpro/files/devkitARM/
I tried a lot of those prebuilt toolchains and found the one from Sourcery CodeBench [1] to be the fastest: Compiling a medium sized project on Windows is about twice as fast with the Sourcery CodeBench toolchain compared to the on mentioned in this posting.
I followed [2][3][4] to setup Eclipse to have a free and unrestricted compile/debug environment.
[1] https://sourcery.mentor.com/sgpp/lite/arm/portal/subscription?@template=lite
[2] http://shareee.netne.net/wordpress/?p=5
[3] https://sites.google.com/site/stm32discovery/open-source-development-with-the-stm32-discovery/setting-up-eclipse-for-stm32-discovery-development
[4] https://sites.google.com/site/stm32discovery/open-source-development-with-the-stm32-discovery/getting-hardware-debuging-working-with-eclipse-and-code-sourcey
@Markus: those sites really helped me! Did anyone have any success with Indigo and GNU ARM eclipse plugin?
@ZotDitzMyo: It worked fine for me.
There’s also a Homebrew wrapper for this toolchain available in the MikeSmith/misc tap.