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.

Don't link to Win32 library libstdc++

diff --git "a/meson.build" "b/meson.build"
index eaaca7f..9b9d2d3 100644
--- "a/meson.build"	
+++ "b/meson.build"
@@ -1030,8 +1030,7 @@ if host_machine.system() == 'windows'
     add_project_link_arguments(
       '-Wl,--nxcompat',
       '-Wl,--dynamicbase',
       '-static-libgcc',
-      '-static-libstdc++',
       language : ['c', 'cpp'],
     )
   endif