bind.py: upgrade llvm version

[masinag]

bind.py downloads llvm version 6.0.1 that forces the usage of Python 2 (see, e.g., this post)

In fact, by compiling the library I get

CMake Error at CMakeLists.txt:606 (if):
  if given arguments:

    "VERSION_LESS" "2.7"

  Unknown arguments specified

That is originated from the following lines in build/llvm-6.0.1/CMakeLists.txt:

# Verify that we can find a Python 2 interpreter.  Python 3 is unsupported.
# FIXME: We should support systems with only Python 3, but that requires work
# on LLDB.
set(Python_ADDITIONAL_VERSIONS 2.7)
include(FindPythonInterp)
if( NOT PYTHONINTERP_FOUND )
  message(FATAL_ERROR
"Unable to find Python interpreter, required for builds and testing.

Please install Python or specify the PYTHON_EXECUTABLE CMake variable.")
endif()

if( ${PYTHON_VERSION_STRING} VERSION_LESS 2.7 )
  message(FATAL_ERROR "Python 2.7 or newer is required")
endif()

[lyskov]

Hm... unfortunately I have to keep LLVM-6 as default since that the last LLVM version that can be build on CentOS-7 with default compiler. How about adding command line flag to the build script that will allow user to specify LLVM version to use?

[masinag]

I can open a PR trying to add a command line flag.
I would raise an error if the version is not specified when using python3, since the error message given by CMake is not clear at all and I had to dig into LLVM source files to understand the origin of the error :)

[lyskov]

I can open a PR trying to add a command line flag. I would raise an error if the version is not specified when using python3, since the error message given by CMake is not clear at all and I had to dig into LLVM source files to understand the origin of the error :)

-- sounds good, - thank you!