Reorder FindPythonInterp so that config-ix can use PYTHON_EXECUTABLE

[lanza]

Summary

Code in config-ix tries to call PYTHON_EXECUTABLE to search for some
python modules but that variable isn't set until the moved chunk of
code that finds Python is called.

Reorder it so CMake can use PYTHON_EXECUTABLE

[rnk]

I was going to consult @zturner about the state of Python 3 in LLDB, but that's not really related to your change. I think it's fine. lgtm

[lanza]

Yea, unrelated to python3. Just a trivial fix to stop the cannot find pygments in the cmake invocation due to not having PYTHON_EXECUTABLE defined at that point.

llvm/trunk/CMakeLists.txt

 
 # Override the default target with an environment variable named by LLVM_TARGET_TRIPLE_ENV.
 set(LLVM_TARGET_TRIPLE_ENV CACHE STRING "The name of environment variable to override default target. Disabled by blank.")
 mark_as_advanced(LLVM_TARGET_TRIPLE_ENV)
 
 set(LLVM_ENABLE_PER_TARGET_RUNTIME_DIR OFF CACHE BOOL
   "Enable per-target runtimes directory")
 
+# 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()
+
 # All options referred to from HandleLLVMOptions have to be specified
 # BEFORE this include, otherwise options will not be correctly set on
 # first cmake run
 include(config-ix)
 
 string(REPLACE "Native" ${LLVM_NATIVE_ARCH}
   LLVM_TARGETS_TO_BUILD "${LLVM_TARGETS_TO_BUILD}")
 list(REMOVE_DUPLICATES LLVM_TARGETS_TO_BUILD)
 
 # By default, we target the host, but this can be overridden at CMake
 # invocation time.
 set(LLVM_DEFAULT_TARGET_TRIPLE "${LLVM_HOST_TRIPLE}" CACHE STRING
   "Default target for which LLVM will generate code." )
 set(TARGET_TRIPLE "${LLVM_DEFAULT_TARGET_TRIPLE}")
 message(STATUS "LLVM host triple: ${LLVM_HOST_TRIPLE}")
 message(STATUS "LLVM default target triple: ${LLVM_DEFAULT_TARGET_TRIPLE}")
 
 include(HandleLLVMOptions)
 
-# 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()
-
 ######
 # LLVMBuild Integration
 #
 # We use llvm-build to generate all the data required by the CMake based
 # build system in one swoop:
 #
 #  - We generate a file (a CMake fragment) in the object root which contains
 #    all the definitions that are required by CMake.