I failed in trying to get a build of clang crosscompiling it via javacom's toolchain4. The fail is at the build-tools phase (the first stem for those who dared building a compiler. It's intended to create some needed utils, such as llvm-tblgen, or cgcc in gcc's case).
I'd like to add that I got the set fault above when trying to build clang on an iPad2 while using dynamic_page. I had to as the build of some files would exceed the amount of ram available, killing gcc before it could create the output. If someone has a newer/bett device, he/she might give a try and see how far can go. I suggest connecting the device via USB and using iPhoneTunnel or apps alike to spare some more ram (a wifi/direct ssh would use much more ram than this way).
edit: on the use of currently built clang: one of my guesses lead me to think that clang needs a flag to know what architecture it has to build. According to llvm-config --targets-built, there are more than one.
clang DO NOT accept the -arch flag. In its place -ccc-host-triple armv7-apple-darwin11 should be used (this one was an example). Even with this new info I can't get it to build without having the undefined symbol dyld_stub_ binding_helper
edit 2: Be sure to specify armv as the simple arm build for architecture armv4t.