Don't attempt to upgrade debug-info-tests to Python3.

There was CMake code that would attempt to detect Python 3 even if
LLVM was configured with Python 2, but it messed with the environment
for the other LLVM projects. This commit removes this functionality
and just lkeaves a hard error if Python < 3 is detected and
debuginfo-tests are required.

Author: adrian-prantl

debuginfo-tests/CMakeLists.txt

@@ -18,26 +18,6 @@ if (WIN32)
   set(DEBUGINFO_TEST_DEPS ${DEBUGINFO_TEST_DEPS} lld)
 endif()
 
-# If we don't already have Python 3, throw away any previous results and try to
-# find it again.
-set(DEBUGINFO_UNSET_PYTHON3 OFF)
-if (PYTHON_VERSION_MAJOR LESS 3)
-  unset(PYTHONINTERP_FOUND CACHE)
-  unset(PYTHON_EXECUTABLE CACHE)
-  unset(PYTHON_LIBRARY CACHE)
-  unset(PYTHON_DLL CACHE)
-  unset(PYTHON_INCLUDE_DIR CACHE)
-  unset(PYTHON_VERSION_STRING CACHE)
-  unset(PYTHON_VERSION_MAJOR CACHE)
-  unset(PYTHON_VERSION_MINOR CACHE)
-  unset(PYTHON_VERSION_PATCH CACHE)
-  unset(PYTHONLIBS_VERSION_STRING CACHE)
-
-  # Try to find python3. If it doesn't exist, dexter tests can't run.
-  find_package(PythonInterp "3")
-  set(DEBUGINFO_UNSET_PYTHON3 ON)
-endif()
-
 if (NOT DEFINED PYTHON_EXECUTABLE)
   message(FATAL_ERROR "Cannot run debuginfo-tests without python")
 elseif(PYTHON_VERSION_MAJOR LESS 3)
@@ -56,18 +36,3 @@ else()
     )
   set_target_properties(check-debuginfo PROPERTIES FOLDER "Debug info tests")
 endif()
-
-# Prevent the rest of llvm observing our secret python3-ness, if that wasn't
-# what was originally found.
-if (DEBUGINFO_UNSET_PYTHON3)
-  unset(PYTHONINTERP_FOUND CACHE)
-  unset(PYTHON_EXECUTABLE CACHE)
-  unset(PYTHON_LIBRARY CACHE)
-  unset(PYTHON_DLL CACHE)
-  unset(PYTHON_INCLUDE_DIR CACHE)
-  unset(PYTHON_VERSION_STRING CACHE)
-  unset(PYTHON_VERSION_MAJOR CACHE)
-  unset(PYTHON_VERSION_MINOR CACHE)
-  unset(PYTHON_VERSION_PATCH CACHE)
-  unset(PYTHONLIBS_VERSION_STRING CACHE)
-endif()