Add build rule for build-octave (bug #49503). * src/build-octave.mk: Add new build rule for build-octave which can be used for cross-building binary packages that depend on Octave as a build tool. * dist-files.mk: Add new file to list. * index.html: Add new package to list. * src/of-communications.mk, src/of-image.mk, src/of-mapping.mk, src/of-optiminterp.mk, src/of-sparsersb.mk, src/of-statistics.mk, src/of-windows.mk: Add optional dependency on build-octave. * configure.ac: Add new configure switch "--disable-system-octave" that is needed to build the build-octave package. * Makefile.in: Add variable "USE_SYSTEM_OCTAVE". Exclude build-octave from the default build tools and build it only if a package explicitly depends on it. Display warning about missing native Octave version only if necessary.

diff -ru gl2ps-1.4.2.orig/CMakeLists.txt gl2ps-1.4.2/CMakeLists.txt
--- gl2ps-1.4.2.orig/CMakeLists.txt	2020-04-25 16:44:55.536814745 -0400
+++ gl2ps-1.4.2/CMakeLists.txt	2020-05-07 19:08:35.538729120 -0400
@@ -156,7 +156,7 @@
                              ARCHIVE DESTINATION lib${LIB_SUFFIX})
 endif()
 
-if(WIN32)
+if(WIN32 AND NOT DEFINED ENV{MSYSTEM})
   set(GL2PS_DOC .)
 else()
   set(GL2PS_DOC share/doc/gl2ps)