[flang] Use `GNUInstallDirs` to support custom installation dirs.

Extracted from D99484. My new plan is to start from the outside and work
inward.

Reviewed By: stephenneuendorffer

Differential Revision: https://reviews.llvm.org/D115569

flang/CMakeLists.txt

@@ -7,6 +7,8 @@ set(CMAKE_CXX_STANDARD 17)
 set(CMAKE_CXX_STANDARD_REQUIRED TRUE)
 set(CMAKE_CXX_EXTENSIONS OFF)
 
+include(GNUInstallDirs)
+
 set(FLANG_SOURCE_DIR ${CMAKE_CURRENT_SOURCE_DIR})
 
 if (CMAKE_SOURCE_DIR STREQUAL CMAKE_BINARY_DIR AND NOT MSVC_IDE)
@@ -226,7 +228,10 @@ include_directories(BEFORE
   ${FLANG_SOURCE_DIR}/include)
 
 # Add Flang-centric modules to cmake path.
-list(APPEND CMAKE_MODULE_PATH "${CMAKE_CURRENT_SOURCE_DIR}/cmake/modules")
+list(INSERT CMAKE_MODULE_PATH 0
+  "${FLANG_SOURCE_DIR}/cmake/modules"
+  "${FLANG_SOURCE_DIR}/../cmake/Modules"
+  )
 include(AddFlang)
 
 if (NOT DEFAULT_SYSROOT)
@@ -444,7 +449,7 @@ endif()
 
 if (NOT LLVM_INSTALL_TOOLCHAIN_ONLY)
   install(DIRECTORY include/flang
-    DESTINATION include
+    DESTINATION "${CMAKE_INSTALL_INCLUDEDIR}"
     COMPONENT flang-headers
     FILES_MATCHING
     PATTERN "*.def"
@@ -456,7 +461,7 @@ if (NOT LLVM_INSTALL_TOOLCHAIN_ONLY)
     PATTERN "CMakeFiles" EXCLUDE)
     
   install(DIRECTORY ${FLANG_INCLUDE_DIR}/flang
-    DESTINATION include
+    DESTINATION "${CMAKE_INSTALL_INCLUDEDIR}"
     COMPONENT flang-headers
     FILES_MATCHING
     PATTERN "*.inc"

flang/cmake/modules/AddFlang.cmake

@@ -1,3 +1,4 @@
+include(GNUInstallDirs)
 include(LLVMDistributionSupport)
 
 macro(set_flang_windows_version_resource_properties name)
@@ -71,7 +72,7 @@ macro(add_flang_library name)
         ${export_to_flangtargets}
         LIBRARY DESTINATION lib${LLVM_LIBDIR_SUFFIX}
         ARCHIVE DESTINATION lib${LLVM_LIBDIR_SUFFIX}
-        RUNTIME DESTINATION bin)
+        RUNTIME DESTINATION "${CMAKE_INSTALL_BINDIR}")
 
       if (NOT LLVM_ENABLE_IDE)
         add_llvm_install_targets(install-${name}
@@ -108,7 +109,7 @@ macro(add_flang_tool name)
     get_target_export_arg(${name} Flang export_to_flangtargets)
     install(TARGETS ${name}
       ${export_to_flangtargets}
-      RUNTIME DESTINATION bin
+      RUNTIME DESTINATION "${CMAKE_INSTALL_BINDIR}"
       COMPONENT ${name})
 
     if(NOT LLVM_ENABLE_IDE)

flang/cmake/modules/CMakeLists.txt

@@ -1,3 +1,5 @@
+include(ExtendPath)
+
 # 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 ${Project}Targets.cmake.
@@ -41,7 +43,7 @@ endforeach(p)
 set(FLANG_CONFIG_CMAKE_DIR "\${FLANG_INSTALL_PREFIX}/${FLANG_INSTALL_PACKAGE_DIR}")
 set(FLANG_CONFIG_LLVM_CMAKE_DIR "\${FLANG_INSTALL_PREFIX}/${LLVM_INSTALL_PACKAGE_DIR}")
 get_config_exports_includes(Flang FLANG_CONFIG_INCLUDE_EXPORTS)
-set(FLANG_CONFIG_INCLUDE_DIRS "\${FLANG_INSTALL_PREFIX}/include")
+extend_path(FLANG_CONFIG_INCLUDE_DIRS "\${FLANG_INSTALL_PREFIX}" "${CMAKE_INSTALL_INCLUDEDIR}")
 
 configure_file(
   ${CMAKE_CURRENT_SOURCE_DIR}/FlangConfig.cmake.in

flang/tools/f18/CMakeLists.txt

@@ -38,7 +38,7 @@ foreach(filename ${MODULES})
     DEPENDS ${base}.mod
     COMMAND ${CMAKE_COMMAND} -E copy ${base}.mod ${base}.f18.mod)
   list(APPEND MODULE_FILES ${base}.mod ${base}.f18.mod)
-  install(FILES ${base}.mod ${base}.f18.mod DESTINATION include/flang)
+  install(FILES ${base}.mod ${base}.f18.mod DESTINATION "${CMAKE_INSTALL_INCLUDEDIR}/flang")
 endforeach()
 
 add_custom_target(module_files ALL DEPENDS ${MODULE_FILES})
@@ -48,5 +48,5 @@ if (NOT WIN32)
   file(COPY ${CMAKE_CURRENT_SOURCE_DIR}/flang
     DESTINATION ${CMAKE_BINARY_DIR}/bin
     FILE_PERMISSIONS OWNER_EXECUTE OWNER_READ OWNER_WRITE)
-  install(PROGRAMS ${CMAKE_BINARY_DIR}/bin/flang DESTINATION bin)
+  install(PROGRAMS ${CMAKE_BINARY_DIR}/bin/flang DESTINATION "${CMAKE_INSTALL_BINDIR}")
 endif()

flang/tools/flang-driver/CMakeLists.txt

@@ -34,4 +34,4 @@ if(FLANG_PLUGIN_SUPPORT)
   export_executable_symbols_for_plugins(flang-new)
 endif()
 
-install(TARGETS flang-new DESTINATION bin)
+install(TARGETS flang-new DESTINATION "${CMAKE_INSTALL_BINDIR}")