[CMake] Find python before searching for python modules

In the top-level llvm `CMakeLists.txt`, we need to call
`find_package(Python3)` *before* including `config-ix.cmake`, otherwise
the latter will not be able to successfully search for python modules
using `find_python_module()`. Also set `LLVM_MINIMUM_PYTHON_VERSION`
before calling `find_package(Python3)`, moving it to `CMakeLists.txt`
from `HandleLLVMOptions.cmake`.

Reviewed By: compnerd

Differential Revision: https://reviews.llvm.org/D131191

GitOrigin-RevId: 45c056b1fb5a9bc797e935b160aa07bf53764a3a
2 files changed