[CMake] find python should before include cmake-ix

[SquallATF]

Summary

because cmake-ix use Python3_EXECUTABLE before it defined.

[mgorny]

I suppose this makes sense and shouldn't break anything.

llvm/CMakeLists.txt

 mark_as_advanced(LLVM_TARGET_TRIPLE_ENV)
 
 set(LLVM_ENABLE_PER_TARGET_RUNTIME_DIR OFF CACHE BOOL
   "Enable per-target runtimes directory")
 
 set(LLVM_PROFDATA_FILE "" CACHE FILEPATH
   "Profiling data file to use when compiling in order to improve runtime performance.")
 
-# 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}")
-
-if(WIN32 OR CYGWIN)
-  if(BUILD_SHARED_LIBS OR LLVM_BUILD_LLVM_DYLIB)
-    set(LLVM_ENABLE_PLUGINS_default ON)
-  else()
-    set(LLVM_ENABLE_PLUGINS_default OFF)
-  endif()
-else()
-  set(LLVM_ENABLE_PLUGINS_default ${LLVM_ENABLE_PIC})
-endif()
-option(LLVM_ENABLE_PLUGINS "Enable plugin support" ${LLVM_ENABLE_PLUGINS_default})
-
-include(HandleLLVMOptions)
-
 if(CMAKE_VERSION VERSION_LESS 3.12)
   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(NOT Python3_Interpreter_FOUND)
     # Treat python2 as python3
     add_executable(Python3::Interpreter IMPORTED)
     set_target_properties(Python3::Interpreter PROPERTIES
       IMPORTED_LOCATION ${Python2_EXECUTABLE})
     set(Python3_EXECUTABLE ${Python2_EXECUTABLE})
   endif()
 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}")
+
+if(WIN32 OR CYGWIN)
+  if(BUILD_SHARED_LIBS OR LLVM_BUILD_LLVM_DYLIB)
+    set(LLVM_ENABLE_PLUGINS_default ON)
+  else()
+    set(LLVM_ENABLE_PLUGINS_default OFF)
+  endif()
+else()
+  set(LLVM_ENABLE_PLUGINS_default ${LLVM_ENABLE_PIC})
+endif()
+option(LLVM_ENABLE_PLUGINS "Enable plugin support" ${LLVM_ENABLE_PLUGINS_default})
+
+include(HandleLLVMOptions)
+
 ######
 # 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.