CMake: use CMAKE_INSTALL_FULL_INCLUDEDIR

Users may want to provide absolute paths in `CMAKE_INSTALL_INCLUDEDIR`.
When this is the case, we should not prefix it in any way.

To deal with this use case, use `CMAKE_INSTALL_FULL_*DIR` instead, ref.
https://cmake.org/cmake/help/latest/module/GNUInstallDirs.html#result-variables

Author: nim65s

install/PackageConfig.cmake.in

@@ -25,15 +25,15 @@ endif()
 
 if(NOT TARGET zenohcxx)
 	add_library(zenohcxx INTERFACE IMPORTED)
-	target_include_directories(zenohcxx INTERFACE "${_IMPORT_PREFIX}/@CMAKE_INSTALL_INCLUDEDIR@")
+	target_include_directories(zenohcxx INTERFACE "@CMAKE_INSTALL_FULL_INCLUDEDIR@")
 endif()
 
 # zenohcxx for zenohpico
 if(TARGET zenohpico::lib AND NOT TARGET zenohcxx_zenohpico)
 	message(STATUS "defined lib target zenohcxx::zenohpico for zenohpico::lib")
 	add_library(zenohcxx_zenohpico INTERFACE IMPORTED)
 	target_compile_definitions(zenohcxx_zenohpico INTERFACE ZENOHCXX_ZENOHPICO)
-    target_include_directories(zenohcxx_zenohpico INTERFACE "${_IMPORT_PREFIX}/@CMAKE_INSTALL_INCLUDEDIR@")
+	target_include_directories(zenohcxx_zenohpico INTERFACE "@CMAKE_INSTALL_FULL_INCLUDEDIR@")
 	add_dependencies(zenohcxx_zenohpico zenohpico::lib)
 	target_link_libraries(zenohcxx_zenohpico INTERFACE zenohpico::lib)
 	add_library(zenohcxx::zenohpico ALIAS zenohcxx_zenohpico)
@@ -44,7 +44,7 @@ if(TARGET zenohc::lib AND NOT TARGET zenohcxx_zenohc)
 	message(STATUS "defined lib target zenohcxx::zenohc for zenohc::lib")
 	add_library(zenohcxx_zenohc INTERFACE IMPORTED)
 	target_compile_definitions(zenohcxx_zenohc INTERFACE ZENOHCXX_ZENOHC)
-    target_include_directories(zenohcxx_zenohc INTERFACE "${_IMPORT_PREFIX}/@CMAKE_INSTALL_INCLUDEDIR@")
+	target_include_directories(zenohcxx_zenohc INTERFACE "@CMAKE_INSTALL_FULL_INCLUDEDIR@")
 	add_dependencies(zenohcxx_zenohc zenohc::lib)
 	target_link_libraries(zenohcxx_zenohc INTERFACE zenohc::lib)
 	add_library(zenohcxx::zenohc ALIAS zenohcxx_zenohc)

install/zenohcxx.pc.in

@@ -4,4 +4,4 @@ Name: @PROJECT_NAME@
 Description: @CMAKE_PROJECT_DESCRIPTION@
 URL: @CMAKE_PROJECT_HOMEPAGE_URL@
 Version: @PROJECT_VERSION@
-Cflags: -I${prefix}/@CMAKE_INSTALL_INCLUDEDIR@
+Cflags: -I@CMAKE_INSTALL_FULL_INCLUDEDIR@