[mlir][Python] Adapt to include property change in pybind11 v2.6.

[stellaraccident]

Fix typo.

mlir/CMakeLists.txt

set(MLIR_BINDINGS_PYTHON_ENABLED 0 CACHE BOOL
        "Enables building of Python bindings.")
 set(MLIR_PYTHON_BINDINGS_VERSION_LOCKED 1 CACHE BOOL
        "Links to specific python libraries, resolving all symbols.")
 
 if(MLIR_BINDINGS_PYTHON_ENABLED)
   find_package(PythonInterp REQUIRED)
   find_package(PythonLibs REQUIRED)
   message(STATUS "Found python include dirs: ${PYTHON_INCLUDE_DIRS}")
-  message(STATUS "Found ppython libraries: ${PYTHON_LIBRARIES}")
+  message(STATUS "Found python libraries: ${PYTHON_LIBRARIES}")
   find_package(pybind11 CONFIG REQUIRED)
-  message(STATUS "Found pybind11 v${pybind11_VERSION}: ${pybind11_INCLUDE_DIRS}")
+  # TODO: pybind11 v2.6 switched from pybind11_INCLUDE_DIRS (plural) to
+  # pybind11_INCLUDE_DIR (singular). A lot has changed in this area since this
+  # was written and overall python config and pybind11 should be modernized.
+  set(pybind11_INCLUDE_DIR ${pybind11_INCLUDE_DIR} ${pybind11_INCLUDE_DIRS})
+  message(STATUS "Found pybind11 v${pybind11_VERSION}: ${pybind11_INCLUDE_DIR}")
   message(STATUS "Python prefix = '${PYTHON_MODULE_PREFIX}', "
                  "suffix = '${PYTHON_MODULE_SUFFIX}', "
                  "extension = '${PYTHON_MODULE_EXTENSION}")
 endif()
 
 include_directories( "include")
 include_directories( ${MLIR_INCLUDE_DIR})
 

mlir/cmake/modules/AddMLIRPythonExtension.cmake

function(add_mlir_python_extension libname extname)
   # sources that must be compiled in accordance with pybind11 needs (RTTI and
   # exceptions).
   add_library(${libname} ${PYEXT_LINK_MODE}
     ${ARG_SOURCES}
   )
 
   target_include_directories(${libname} PRIVATE
     "${PYTHON_INCLUDE_DIRS}"
-    "${pybind11_INCLUDE_DIRS}"
+    "${pybind11_INCLUDE_DIR}"
   )
 
   # The extension itself must be compiled with RTTI and exceptions enabled.
   # Also, some warning classes triggered by pybind11 are disabled.
   target_compile_options(${libname} PRIVATE
     $<$<OR:$<CXX_COMPILER_ID:Clang>,$<CXX_COMPILER_ID:AppleClang>,$<CXX_COMPILER_ID:GNU>>:
       # Enable RTTI and exceptions.
       -frtti -fexceptions