While that may not work in some environments that don't support these extensions, I'm having trouble imagining ones that support C stdio but do not support linker sets.
My primary goal with greatest is to assume as little as possible, and avoid imposing any additional constraints on projects just because people want to test them. I also want the implementation to be very transparent -- it's just a 600-ish line header file, carefully documented. It's a major pet peeve of mine when I have to work around features that try to automatically be helpful, but have edge cases that break down in opaque ways. (Build systems tend to be particularly bad in that way.)
Also, I'm beyond shocked that the name wasn't already taken. ;)
One of my upcoming tasks is making stdio optional in greatest, because printf doesn't do you a whole lot of good if you're running it on an Arduino or something, but in those contexts automated testing is especially valuable.
The test C test framework in the project is 4 lines long, but does require the standard library. https://github.com/meekrosoft/fff/blob/master/test/c_test_fr...
I've tended to use CMock (https://github.com/ThrowTheSwitch/CMock) for mocking, though it depends on some Ruby-based tooling. The last time I looked into replacing CMock I wound up hip-deep in the binutils. (It was fun when I stopped getting google results from StackOverflow and started getting them from Phrack, though. ;) )
It was the most featureful that I found when I was looking last year.