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             := mingwrt
$(PKG)_IGNORE   :=
$(PKG)_VERSION  := 3.20-2
$(PKG)_CHECKSUM := cc6c1f841ab255e52e60f9c967cea6acf29354db
$(PKG)_SUBDIR   := .
$(PKG)_FILE     := $(PKG)-$($(PKG)_VERSION)-mingw32-dev.tar.lzma
$(PKG)_URL      := http://$(SOURCEFORGE_MIRROR)/project/mingw/MinGW/Base/mingw-rt/mingwrt-3.20/$($(PKG)_FILE)
$(PKG)_DEPS     :=

define $(PKG)_UPDATE
    $(WGET) -q -O- 'https://sourceforge.net/projects/mingw/files/MinGW/Base/mingwrt/' | \
    $(SED) -n 's,.*mingwrt-\([0-9][^"]*\)/".*,\1,p' | \
    head -1
endef

define $(PKG)_BUILD
    $(INSTALL) -d '$(HOST_PREFIX)'
    cd '$(1)' && \
        cp -rpv include lib '$(HOST_PREFIX)'
endef