[mlir][python] Install precise pattern for generated files.

[stellaraccident]

Summary

Previously, this was matching all linked files in the build tree, including generated files. When we switched to symlinks and added non generated files, this broke the Windows install: CMake seems to have trouble installing symlinks on Windows. Since this was not intended, just fixed the too broad of a match.

[stellaraccident]

Submitting this as is since it is breaking the windows build. Feel free to post review.

mlir/lib/Bindings/Python/CMakeLists.txt

SOURCES
     PybindUtils.cpp
     Pass.cpp
     ExecutionEngine.cpp
 )
 add_dependencies(MLIRBindingsPythonExtension MLIRCoreBindingsPythonExtension)
 
 # Note that we copy from the source tree just like for headers because
 # it will not be polluted with py_cache runtime artifacts (from testing and
-# such).
+# such). Note that Windows has trouble installing symlinks, which makes it
+# necessary to install these from the source tree.
 install(
   DIRECTORY ${CMAKE_CURRENT_SOURCE_DIR}/mlir
   DESTINATION python
   COMPONENT MLIRBindingsPythonSources
   FILES_MATCHING PATTERN "*.py"
 )
 
 if (NOT LLVM_ENABLE_IDE)
   add_llvm_install_targets(
     install-MLIRBindingsPythonSources
     DEPENDS MLIRBindingsPythonSources
     COMPONENT MLIRBindingsPythonSources)
 endif()
 
-# Dialect sources are generated. Install separately.
-# Note that __pycache__ directories may have been left by tests and other
-# executions. And __init__.py is handled as a regular source file.
+# Install generated dialect sources, all of which have the same file name
+# pattern (and must not match any source file patterns).
 install(
   DIRECTORY ${PROJECT_BINARY_DIR}/python/mlir/dialects
   DESTINATION python/mlir
   COMPONENT MLIRBindingsPythonDialects
-  FILES_MATCHING PATTERN "*.py"
+  FILES_MATCHING PATTERN "_*_gen.py"
   PATTERN "__pycache__" EXCLUDE
   PATTERN "__init__.py" EXCLUDE
 )
 
 if (NOT LLVM_ENABLE_IDE)
   add_llvm_install_targets(
     install-MLIRBindingsPythonDialects
     DEPENDS MLIRBindingsPythonSources
     COMPONENT MLIRBindingsPythonDialects)
 endif()
 
 add_subdirectory(Transforms)
 add_subdirectory(Conversions)