lldb: PYTHON_EXECUTABLE should be propagated more carefully

[pawelo]

Summary

This is one of two problems I encountered when I tried to build and install lldb on Gentoo Linux where default Python interpreter is version 3.3.
To force use of Python 2.7 which lldb requires, one has to type cmake -DPYTHON_EXECUTABLE=/usr/bin/python2.7
Unfortunately, it seems like this option is not propagated properly and 'make install' still uses /usr/bin/python to determine interpreter version.
Proposed patch fixes this weird behaviour.

[pawelo]

Obsoleted by upstream improvements.

scripts/CMakeLists.txt

 set_source_files_properties(${CMAKE_CURRENT_BINARY_DIR}/LLDBWrapPython.cpp PROPERTIES GENERATED 1)
 
 ADD_CUSTOM_TARGET(swig_wrapper ALL echo -n
     DEPENDS ${CMAKE_CURRENT_BINARY_DIR}/LLDBWrapPython.cpp
     )
 
 # Install the LLDB python module on all operating systems (except Windows)
 if (NOT CMAKE_SYSTEM_NAME MATCHES "Windows")
-  install(SCRIPT lldb_python_module.cmake -DCMAKE_INSTALL_PREFIX=\"${CMAKE_INSTALL_PREFIX}\" -DCMAKE_BUILD_DIR=\"${CMAKE_BUILD_DIR}\")
+  configure_file(lldb_python_module.cmake ${CMAKE_CURRENT_BINARY_DIR}/lldb_python_module.cmake @ONLY)
+  install(SCRIPT ${CMAKE_CURRENT_BINARY_DIR}/lldb_python_module.cmake -DCMAKE_INSTALL_PREFIX=\"${CMAKE_INSTALL_PREFIX}\" -DCMAKE_BUILD_DIR=\"${CMAKE_BUILD_DIR}\" -DPYTHON_EXECUTABLE=\"${PYTHON_EXECUTABLE}\")
 endif()
 
 # build Python modules
 add_subdirectory(Python/modules)

scripts/lldb_python_module.cmake

 # This CMake script installs the LLDB python module from the build directory
 # to the install directory.
 
+SET(PYTHON_EXECUTABLE "@PYTHON_EXECUTABLE@")
+
 # FIXME: if a non-standard version of python is requested, the cmake macro
 # below will need Python_ADDITIONAL_VERSIONS set in order to find it.
 include(FindPythonInterp)
 
 SET(PYTHON_DIRECTORY python${PYTHON_VERSION_MAJOR}.${PYTHON_VERSION_MINOR})
 
 SET(lldb_module_src ${CMAKE_CURRENT_BINARY_DIR}/lib/${PYTHON_DIRECTORY})
 SET(lldb_module_dest "$ENV{DESTDIR}${CMAKE_INSTALL_PREFIX}/lib")
 
 MESSAGE(STATUS "Installing LLDB python module from: ${lldb_module_src} to ${lldb_module_dest}")
 FILE(COPY "${lldb_module_src}" DESTINATION "${lldb_module_dest}")