allow absolute CMAKE_INSTALL_*DIR (#2134)

This patch fixes Capstone 5 build on NixOS.

NixOS's build infrastructure sets CMAKE_INSTALL_{LIB,INCLUDE}DIR to
absolute paths. If you append it to ${prefix}, you get the wrong path.
NixOS automatically detects it and links this issue:
NixOS/nixpkgs#144170

capstone-config.cmake.in

@@ -1,6 +1,6 @@
 @PACKAGE_INIT@
 
-set_and_check(capstone_INCLUDE_DIR "${PACKAGE_PREFIX_DIR}/@CMAKE_INSTALL_INCLUDEDIR@")
-set_and_check(capstone_LIB_DIR "${PACKAGE_PREFIX_DIR}/@CMAKE_INSTALL_LIBDIR@")
+set_and_check(capstone_INCLUDE_DIR "@CMAKE_INSTALL_FULL_INCLUDEDIR@")
+set_and_check(capstone_LIB_DIR "@CMAKE_INSTALL_FULL_LIBDIR@")
 
 include("${CMAKE_CURRENT_LIST_DIR}/capstone-targets.cmake")

capstone.pc.in

@@ -1,7 +1,7 @@
 prefix=@CMAKE_INSTALL_PREFIX@
 exec_prefix=${prefix}
-libdir=${prefix}/@CMAKE_INSTALL_LIBDIR@
-includedir=${prefix}/@CMAKE_INSTALL_INCLUDEDIR@
+libdir=@CMAKE_INSTALL_FULL_LIBDIR@
+includedir=@CMAKE_INSTALL_FULL_INCLUDEDIR@
 
 Name: capstone
 Description: Capstone disassembly engine

cmake_uninstall.cmake.in

@@ -13,8 +13,8 @@ foreach(file ${files})
   endif()
 endforeach()
 
-message(STATUS "Uninstalling @CMAKE_INSTALL_PREFIX@/@CMAKE_INSTALL_INCLUDEDIR@/capstone")
-file(REMOVE_RECURSE @CMAKE_INSTALL_PREFIX@/@CMAKE_INSTALL_INCLUDEDIR@/capstone)
+message(STATUS "Uninstalling @CMAKE_INSTALL_FULL_INCLUDEDIR@/capstone")
+file(REMOVE_RECURSE @CMAKE_INSTALL_FULL_INCLUDEDIR@/capstone)
 
-message(STATUS "Uninstalling @CMAKE_INSTALL_PREFIX@/@CMAKE_INSTALL_LIBDIR@/cmake/capstone")
-file(REMOVE_RECURSE @CMAKE_INSTALL_PREFIX@/@CMAKE_INSTALL_LIBDIR@/cmake/capstone)
+message(STATUS "Uninstalling @CMAKE_INSTALL_FULL_LIBDIR@/cmake/capstone")
+file(REMOVE_RECURSE @CMAKE_INSTALL_FULL_LIBDIR@/cmake/capstone)