I have prepared a version of the Tiny C compiler (tcc) that can run on the Kindle.
You can find it at
http://info.iet.unipi.it/~luigi/kindle/#TCC-for-Kindle
For those who don't know, tcc is a single, small binary that can compile and runs C code on the fly. The only serious impairment (common to all C compilers) is that you often need a ton of headers to build anything useful;
however, i am preparing a workaround which allows you to put all the definitions in a single file and ignore errors for missing headers.
For those who want to give it a try -- the tarball contains the compiler, tcc, and some tiny objects (crt*.o) which you should put in /usr/lib (they are not needed if you just want to run code on the fly).
Then edit your favourite hello world program and run it with
tcc -run helloworld.c