Fix security issue [internal unmaintained JPX decoder] that is caused
by building without system-jpeg libs. Fedora does not care because they
always build with system-jpeg, however in Gentoo we allow the user to
disable both options and poppler's buildsystem is making us believe
there would be no JPX decoder built in that case, when in reality
JPXStream.cc is built (even if it may not be used by the code).


--- a/CMakeLists.txt	2017-11-24 23:12:41.953450442 +0100
+++ b/CMakeLists.txt	2017-11-24 23:16:09.441030669 +0100
@@ -506,9 +508,11 @@
   add_definitions(-DUSE_OPENJPEG2)
   set(poppler_LIBS ${poppler_LIBS} ${LIBOPENJPEG2_LIBRARIES})
 else ()
-  set(poppler_SRCS ${poppler_SRCS}
-    poppler/JPXStream.cc
-  )
+  if(NOT WITH_OPENJPEG AND HAVE_JPX_DECODER)
+    set(poppler_SRCS ${poppler_SRCS}
+      poppler/JPXStream.cc
+    )
+  endif()
 endif()
 if(USE_CMS)
   if(LCMS_FOUND)