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.

# This file is part of MXE.
# See index.html for further information.

PKG             := build-scons
$(PKG)_IGNORE   :=
$(PKG)_VERSION  := 3.1.2
$(PKG)_CHECKSUM := d7541717d503266b37004a33246b6688fe87dec0
$(PKG)_SUBDIR   := scons-$($(PKG)_VERSION)
$(PKG)_FILE     := scons-$($(PKG)_VERSION).tar.gz
$(PKG)_URL      := http://prdownloads.sourceforge.net/scons/$($(PKG)_FILE)
ifeq ($(MXE_NATIVE_MINGW_BUILD),yes)
    $(PKG)_DEPS     := 
else
    $(PKG)_DEPS     := build-python
endif

define $(PKG)_UPDATE
    $(WGET) -q -O- https://sourceforge.net/projects/scons/files/scons/ | \
    $(SED) -n 's|.*<tr title=\"\([0-9][^"]*\)".*|\1|p' | \
    head -1
endef

define $(PKG)_BUILD
    cd '$(1)' && python setup.py install --prefix='$(BUILD_TOOLS_PREFIX)'
endef