[MLIR] Workaround for python detection problems.

Although cmake should be platform-independent, we've observed
that some aspects of Python detection don't work on all platforms,
even with recent versions of cmake.  This appears to be due to bugs
in the python detection logic, especially when the NumPy component
is required and not located within the python installation.
As a workaround, this patch first searches for "Development" before
searching for "Development.Module", which seems to workaround the
issue.

Differential Revision: https://reviews.llvm.org/D118148