Make CMake display more readable paths to Python binaries on Windows

[enlight]

Summary

Previously CMake would display messages like these:

-- LLDB Found PythonExecutable: $<$<CONFIG:Debug>:C:/Projects/Python-2.7.9-bin/x64/python_d.exe>$<$<NOT:$<CONFIG:Debug>>:C:/Projects/Python-2.7.9-bin/x64/python.exe>
-- LLDB Found PythonLibs: $<$<CONFIG:Debug>:C:/Projects/Python-2.7.9-bin/x64/libs/python27_d.lib>$<$<NOT:$<CONFIG:Debug>>:C:/Projects/Python-2.7.9-bin/x64/libs/python27.lib>
-- LLDB Found PythonDLL: $<$<CONFIG:Debug>:C:/Projects/Python-2.7.9-bin/x64/python27_d.dll>$<$<NOT:$<CONFIG:Debug>>:C:/Projects/Python-2.7.9-bin/x64/python27.dll>

This patch makes the messages look like this:

-- LLDB Found PythonExecutable: C:/Projects/Python-2.7.9-bin/x64/python.exe and C:/Projects/Python-2.7.9-bin/x64/python_d.exe
-- LLDB Found PythonLibs: C:/Projects/Python-2.7.9-bin/x64/libs/python27.lib and C:/Projects/Python-2.7.9-bin/x64/libs/python27_d.lib
-- LLDB Found PythonDLL: C:/Projects/Python-2.7.9-bin/x64/python27.dll and C:/Projects/Python-2.7.9-bin/x64/python27_d.dll

I've also added checks to ensure the messages are actually accurate, as in check that the files actually exist before claiming they've been found. If any of the files are missing Python integration will be disabled for the build.

[zturner]

Looks good, thanks.

lldb/trunk/cmake/modules/LLDBConfig.cmake

function(find_python_libs_windows)
   file(TO_CMAKE_PATH "${PYTHON_HOME}/python_d.exe" PYTHON_DEBUG_EXE)
   file(TO_CMAKE_PATH "${PYTHON_HOME}/libs/${PYTHONLIBS_BASE_NAME}_d.lib" PYTHON_DEBUG_LIB)
   file(TO_CMAKE_PATH "${PYTHON_HOME}/${PYTHONLIBS_BASE_NAME}_d.dll" PYTHON_DEBUG_DLL)
 
   file(TO_CMAKE_PATH "${PYTHON_HOME}/python.exe" PYTHON_RELEASE_EXE)
   file(TO_CMAKE_PATH "${PYTHON_HOME}/libs/${PYTHONLIBS_BASE_NAME}.lib" PYTHON_RELEASE_LIB)
   file(TO_CMAKE_PATH "${PYTHON_HOME}/${PYTHONLIBS_BASE_NAME}.dll" PYTHON_RELEASE_DLL)
 
+  if (NOT EXISTS ${PYTHON_DEBUG_EXE})
+    message("Unable to find ${PYTHON_DEBUG_EXE}")
+    unset(PYTHON_DEBUG_EXE)
+  endif()
+
+  if (NOT EXISTS ${PYTHON_RELEASE_EXE})
+    message("Unable to find ${PYTHON_RELEASE_EXE}")
+    unset(PYTHON_RELEASE_EXE)
+  endif()
+
+  if (NOT EXISTS ${PYTHON_DEBUG_LIB})
+    message("Unable to find ${PYTHON_DEBUG_LIB}")
+    unset(PYTHON_DEBUG_LIB)
+  endif()
+
+  if (NOT EXISTS ${PYTHON_RELEASE_LIB})
+    message("Unable to find ${PYTHON_RELEASE_LIB}")
+    unset(PYTHON_RELEASE_LIB)
+  endif()
+
+  if (NOT EXISTS ${PYTHON_DEBUG_DLL})
+    message("Unable to find ${PYTHON_DEBUG_DLL}")
+    unset(PYTHON_DEBUG_DLL)
+  endif()
+
+  if (NOT EXISTS ${PYTHON_RELEASE_DLL})
+    message("Unable to find ${PYTHON_RELEASE_DLL}")
+    unset(PYTHON_RELEASE_DLL)
+  endif()
+
+  if (NOT (PYTHON_DEBUG_EXE AND PYTHON_RELEASE_EXE AND PYTHON_DEBUG_LIB AND PYTHON_RELEASE_LIB AND PYTHON_DEBUG_DLL AND PYTHON_RELEASE_DLL))
+    message("Python installation is corrupt. Python support will be disabled for this build.")
+    set(LLDB_DISABLE_PYTHON 1 PARENT_SCOPE)
+    return()
+  endif()
+
   # Generator expressions are evaluated in the context of each build configuration generated
   # by CMake. Here we use the $<CONFIG:Debug>:VALUE logical generator expression to ensure
   # that the debug Python library, DLL, and executable are used in the Debug build configuration.
   #
   # Generator expressions can be difficult to grok at first so here's a breakdown of the one
   # used for PYTHON_LIBRARY:
   #
   # 1. $<CONFIG:Debug> evaluates to 1 when the Debug configuration is being generated,
function(find_python_libs_windows)
   set (PYTHON_LIBRARY $<$<CONFIG:Debug>:${PYTHON_DEBUG_LIB}>$<$<NOT:$<CONFIG:Debug>>:${PYTHON_RELEASE_LIB}>)
   set (PYTHON_DLL $<$<CONFIG:Debug>:${PYTHON_DEBUG_DLL}>$<$<NOT:$<CONFIG:Debug>>:${PYTHON_RELEASE_DLL}>)
 
   set (PYTHON_EXECUTABLE ${PYTHON_EXECUTABLE} PARENT_SCOPE)
   set (PYTHON_LIBRARY ${PYTHON_LIBRARY} PARENT_SCOPE)
   set (PYTHON_DLL ${PYTHON_DLL} PARENT_SCOPE)
   set (PYTHON_INCLUDE_DIRS ${PYTHON_INCLUDE_DIRS} PARENT_SCOPE)
 
-  message("-- LLDB Found PythonExecutable: ${PYTHON_EXECUTABLE}")
-  message("-- LLDB Found PythonLibs: ${PYTHON_LIBRARY}")
-  message("-- LLDB Found PythonDLL: ${PYTHON_DLL}")
+  message("-- LLDB Found PythonExecutable: ${PYTHON_RELEASE_EXE} and ${PYTHON_DEBUG_EXE}")
+  message("-- LLDB Found PythonLibs: ${PYTHON_RELEASE_LIB} and ${PYTHON_DEBUG_LIB}")
+  message("-- LLDB Found PythonDLL: ${PYTHON_RELEASE_DLL} and ${PYTHON_DEBUG_DLL}")
   message("-- LLDB Found PythonIncludeDirs: ${PYTHON_INCLUDE_DIRS}")
 endfunction(find_python_libs_windows)
 
 if (NOT LLDB_DISABLE_PYTHON)
   if(UNIX)
     # This is necessary for crosscompile on Ubuntu 14.04 64bit. Need a proper fix.
     if(CMAKE_SIZEOF_VOID_P EQUAL 8)
       set(CMAKE_LIBRARY_ARCHITECTURE "x86_64-linux-gnu")