[Cpp] CMake: use variables for specifying install paths consistently (#4109)

* [Cpp] CMake: use variables for specifying install paths consistently

This allows overriding them if needed when the system uses different paths than
usual (e.g. Haiku, which uses "develop/headers" for includes instead of
"include").

Use the standard variable ${CMAKE_INSTALL_INCLUDEDIR} as the base path for the
include directory.

Signed-off-by: Joachim Mairböck <[email protected]>

* [Cpp] CMake: include GNUInstallDirs unconditionally to have CMAKE_INSTALL_DOCDIR available

Signed-off-by: Joachim Mairböck <[email protected]>

---------

Signed-off-by: Joachim Mairböck <[email protected]>

Author: jmairboeck

runtime/Cpp/CMakeLists.txt

@@ -138,10 +138,11 @@ if(WITH_DEMO)
  add_subdirectory(demo)
 endif(WITH_DEMO)
 
+include(GNUInstallDirs)
+
 # Generate CMake Package Files only if install is active
 if (ANTLR4_INSTALL)
 
-  include(GNUInstallDirs)
   include(CMakePackageConfigHelpers)
 
   if(NOT ANTLR4_CMAKE_DIR)
@@ -202,14 +203,14 @@ endif(ANTLR4_INSTALL)
 
 if(EXISTS LICENSE.txt)
 install(FILES LICENSE.txt
-        DESTINATION "share/doc/libantlr4")
+        DESTINATION ${CMAKE_INSTALL_DOCDIR})
 elseif(EXISTS ../../LICENSE.txt)
 install(FILES ../../LICENSE.txt
-    DESTINATION "share/doc/libantlr4")
+    DESTINATION ${CMAKE_INSTALL_DOCDIR})
 endif()
 
 install(FILES README.md VERSION
-    DESTINATION "share/doc/libantlr4")
+    DESTINATION ${CMAKE_INSTALL_DOCDIR})
 
 set(CPACK_PACKAGE_CONTACT "[email protected]")
 set(CPACK_PACKAGE_VERSION ${ANTLR_VERSION})

runtime/Cpp/runtime/CMakeLists.txt

@@ -7,7 +7,7 @@ if (NOT ANTLR_BUILD_SHARED AND NOT ANTLR_BUILD_STATIC)
   message(FATAL_ERROR "Options ANTLR_BUILD_SHARED and ANTLR_BUILD_STATIC can't both be OFF")
 endif()
 
-set(libantlrcpp_INCLUDE_INSTALL_DIR "include/antlr4-runtime")
+set(libantlrcpp_INCLUDE_INSTALL_DIR "${CMAKE_INSTALL_INCLUDEDIR}/antlr4-runtime")
 
 set(libantlrcpp_INCLUDE_DIRS
   ${PROJECT_SOURCE_DIR}/runtime/src