libreoffice: Taking a fix from BLFS for using Glibc 2.23 (isnan is not std::isnan)

pkgs/applications/office/libreoffice/default.nix

···
     patchShebangs .
     # It is used only as an indicator of the proper current directory
     touch solenv/inc/target.mk
+
+    # BLFS patch for Glibc 2.23 renaming isnan
+    sed -ire "s@isnan@std::&@g" xmloff/source/draw/ximp3dscene.cxx
   '';
 
   # fetch_Download_item tries to interpret the name as a variable name