cmake: CMAKE_INSTALL_PREFIX should be evaluated at install stage

Actually CMAKE_INSTALL_PREFIX variable is not properly escape.

This make cmake_install generated file with hardcoded path and
modifying the $prefix at install stage is not usable.

$> cmake --install . --prefix my_prefix

  Could not create symbolic link from
  /usr/local/share/man/man3/pcap_datalink_val_to_name.3pcap

Fix this by properly escaping the CMAKE_INSTALL_PREFIX so the variable
is evaluated at install stage.

Signed-off-by: Clément Péron <peron.clem@gmail.com>

Author: clementperon

CMakeLists.txt

@@ -3301,21 +3301,21 @@ function(install_manpage_symlink SOURCE TARGET MANDIR)
 
     install(CODE "
          if(NOT ${CMAKE_INSTALL_MESSAGE} STREQUAL \"NEVER\")
-             message(STATUS \"Symlinking: \$ENV{DESTDIR}${CMAKE_INSTALL_PREFIX}/${MANDIR}/${SOURCE} to ${TARGET}\")
+             message(STATUS \"Symlinking: \$ENV{DESTDIR}\${CMAKE_INSTALL_PREFIX}/${MANDIR}/${SOURCE} to ${TARGET}\")
          endif()
          execute_process(
             COMMAND \"${CMAKE_COMMAND}\" \"-E\" \"remove\" \"${TARGET}\"
-            WORKING_DIRECTORY \$ENV{DESTDIR}${CMAKE_INSTALL_PREFIX}/${MANDIR}
+            WORKING_DIRECTORY \$ENV{DESTDIR}\${CMAKE_INSTALL_PREFIX}/${MANDIR}
           )
          execute_process(
             COMMAND ${LINK_COMMAND}
-            WORKING_DIRECTORY \$ENV{DESTDIR}${CMAKE_INSTALL_PREFIX}/${MANDIR}
+            WORKING_DIRECTORY \$ENV{DESTDIR}\${CMAKE_INSTALL_PREFIX}/${MANDIR}
             RESULT_VARIABLE EXIT_STATUS
           )
           if(NOT EXIT_STATUS EQUAL 0)
-              message(FATAL_ERROR \"Could not create symbolic link from ${CMAKE_INSTALL_PREFIX}/${MANDIR}/${SOURCE} to ${TARGET}\")
+              message(FATAL_ERROR \"Could not create symbolic link from \${CMAKE_INSTALL_PREFIX}/${MANDIR}/${SOURCE} to ${TARGET}\")
           endif()
-          set(CMAKE_INSTALL_MANIFEST_FILES \${CMAKE_INSTALL_MANIFEST_FILES} ${CMAKE_INSTALL_PREFIX}/${MANDIR}/${TARGET})")
+          set(CMAKE_INSTALL_MANIFEST_FILES \${CMAKE_INSTALL_MANIFEST_FILES} \${CMAKE_INSTALL_PREFIX}/${MANDIR}/${TARGET})")
 endfunction(install_manpage_symlink)
 
 set(MAN1_NOEXPAND pcap-config.1)