[mlir][cmake] Use `GNUInstallDirs` to support custom installation dirs

[Ericson2314]

Summary

I am breaking apart D99484 so the cause of build failures is easier to
understand.

[Ericson2314]

rebase to see how CI is affected

[Ericson2314]

Fix bug

[Ericson2314]

Most this code was already approved in D99484, and the one newer bit is an exact clone of the parts in approved and merged D117541 (for polly), so I am going to merge this to continue my bisecting saga.

mlir/CMakeLists.txt

 # MLIR project.
 
+include(GNUInstallDirs)
+
 # Check if MLIR is built as a standalone project.
 if(CMAKE_SOURCE_DIR STREQUAL CMAKE_CURRENT_SOURCE_DIR)
   project(mlir)
   cmake_minimum_required(VERSION 3.13.4)
 
   find_package(LLVM CONFIG REQUIRED)
   set(CMAKE_MODULE_PATH ${CMAKE_MODULE_PATH} ${LLVM_CMAKE_DIR})
   include(HandleLLVMOptions)

 option(MLIR_INCLUDE_DOCS "Generate build targets for the MLIR docs."
   ${LLVM_INCLUDE_DOCS})
 if (MLIR_INCLUDE_DOCS)
   add_subdirectory(docs)
 endif()
 
 if (NOT LLVM_INSTALL_TOOLCHAIN_ONLY)
   install(DIRECTORY include/mlir include/mlir-c
-    DESTINATION include
+    DESTINATION "${CMAKE_INSTALL_INCLUDEDIR}"
     COMPONENT mlir-headers
     FILES_MATCHING
     PATTERN "*.def"
     PATTERN "*.h"
     PATTERN "*.inc"
     PATTERN "*.td"
     PATTERN "LICENSE.TXT"
     )
 
   install(DIRECTORY ${MLIR_INCLUDE_DIR}/mlir ${MLIR_INCLUDE_DIR}/mlir-c
-    DESTINATION include
+    DESTINATION "${CMAKE_INSTALL_INCLUDEDIR}"
     COMPONENT mlir-headers
     FILES_MATCHING
     PATTERN "*.def"
     PATTERN "*.h"
     PATTERN "*.gen"
     PATTERN "*.inc"
     PATTERN "*.td"
     PATTERN "CMakeFiles" EXCLUDE

mlir/cmake/modules/AddMLIR.cmake

+include(GNUInstallDirs)
 include(LLVMDistributionSupport)
 
 function(mlir_tablegen ofn)
   tablegen(MLIR ${ARGV})
   set(TABLEGEN_OUTPUT ${TABLEGEN_OUTPUT} ${CMAKE_CURRENT_BINARY_DIR}/${ofn}
       PARENT_SCOPE)
   include_directories(${CMAKE_CURRENT_BINARY_DIR})
 endfunction()

 function(add_mlir_library_install name)
   if (NOT LLVM_INSTALL_TOOLCHAIN_ONLY)
   get_target_export_arg(${name} MLIR export_to_mlirtargets UMBRELLA mlir-libraries)
   install(TARGETS ${name}
     COMPONENT ${name}
     ${export_to_mlirtargets}
     LIBRARY DESTINATION lib${LLVM_LIBDIR_SUFFIX}
     ARCHIVE DESTINATION lib${LLVM_LIBDIR_SUFFIX}
-    RUNTIME DESTINATION bin
+    RUNTIME DESTINATION "${CMAKE_INSTALL_BINDIR}"
     # Note that CMake will create a directory like:
     #   objects-${CMAKE_BUILD_TYPE}/obj.LibName
     # and put object files there.
     OBJECTS DESTINATION lib${LLVM_LIBDIR_SUFFIX}
   )
 
   if (NOT LLVM_ENABLE_IDE)
     add_llvm_install_targets(install-${name}

mlir/cmake/modules/CMakeLists.txt

+include(ExtendPath)
 include(LLVMDistributionSupport)
 include(FindPrefixFromConfig)
 
 # Generate a list of CMake library targets so that other CMake projects can
 # link against them. LLVM calls its version of this file LLVMExports.cmake, but
 # the usual CMake convention seems to be ${Project}Targets.cmake.
 set(MLIR_INSTALL_PACKAGE_DIR lib${LLVM_LIBDIR_SUFFIX}/cmake/mlir)
 set(mlir_cmake_builddir "${CMAKE_BINARY_DIR}/${MLIR_INSTALL_PACKAGE_DIR}")
file(COPY .
   PATTERN CMakeFiles EXCLUDE
   )
 
 # Generate MLIRConfig.cmake for the install tree.
 find_prefix_from_config(MLIR_CONFIG_CODE MLIR_INSTALL_PREFIX "${MLIR_INSTALL_PACKAGE_DIR}")
 set(MLIR_CONFIG_CMAKE_DIR "\${MLIR_INSTALL_PREFIX}/${MLIR_INSTALL_PACKAGE_DIR}")
 set(MLIR_CONFIG_LLVM_CMAKE_DIR "\${MLIR_INSTALL_PREFIX}/${LLVM_INSTALL_PACKAGE_DIR}")
 get_config_exports_includes(MLIR MLIR_CONFIG_INCLUDE_EXPORTS)
+extend_path(base_includedir "\${MLIR_INSTALL_PREFIX}" "${CMAKE_INSTALL_INCLUDEDIR}")
 set(MLIR_CONFIG_INCLUDE_DIRS
-  "\${MLIR_INSTALL_PREFIX}/include"
+  "${base_includedir}"
   )
 # Ensure that we are using the installed mlir-tblgen. This might not be MLIR_TABLEGEN_EXE
 # if we're building with a host-optimized mlir-tblgen (with LLVM_OPTIMIZED_TABLEGEN).
 set(MLIR_CONFIG_TABLEGEN_EXE mlir-tblgen)
 
 configure_file(
   ${CMAKE_CURRENT_SOURCE_DIR}/MLIRConfig.cmake.in
   ${CMAKE_CURRENT_BINARY_DIR}/CMakeFiles/MLIRConfig.cmake