ts-merge.c: Added missing includes for stat()

Signed-off-by: Morten Hustveit <morten.hustveit@gmail.com>
Make build scripts more generic

Moved more tests into configure.ac:

  - Check for existence of either llvm-config or llvm-config-3.2
  - Use m4/ax_cxx_compile_stdcxx_11.m4 to check for C++11
  - Use AC_GNU_SOURCE instead of setting -D_GNU_SOURCE in Makefile.am

Signed-off-by: Morten Hustveit <morten.hustveit@gmail.com>
expression-llvm.cc: Made two versions of code, for llvm-3.0 and -3.2

At some point the LLVM project went away from using the const modifier on the
llvm::Type* variables passed to llvm::FunctionType::get.

Signed-off-by: Morten Hustveit <morten.hustveit@gmail.com>