Port to LLVM 3.3

Major changes are:
- Switching to llvm-link to build archive files
- Use GetMallocUsage instead of GetTotalMemoryUsage (be aware of bug in
  LLVM 3.3 http://llvm.org/bugs/show_bug.cgi?id=16847)
- intrinsic library functions like memcpy/mov/set use weak linkage to be
  replaced by e.g. uclibc functions
- rewrote linking with library
- enhanced MemoryLimit test case to check if mallocs were successful
Fixed unused static function warning for forceImport
Fixed multiple definitions of POSIX file functions

Function like stat() were defined for 32bit and 64bit version.
Added compile time based selection of appropriate version
using GNUC macros __x86_64__ and __ppc64__.
Compile separate version of fd files only for LLVM 3.3 or higher
Merge pull request #17 from MartinNowack/LLVM33

Make KLEE compile with LLVM 2.3.