mesalib: Force using Autotools as build system

Work around the warning below, and update to Meson another time.

    configure: error: the autotools build system has been deprecated in favour of
        meson and will be removed eventually. For instructions on how to use meson
        see https://www.mesa3d.org/meson.html.
        If you still want to use the autotools build, then add --enable-autotools
        to the configure command line.

The hunk was not staged to the repository for unknown reasons.

Fixes: commit 7155d7b (mesalib: Update version from 18.3.5 to 19.0.2)

mesalib.be0

@@ -55,6 +55,7 @@ SRCURL[0]="https://mesa.freedesktop.org/archive/mesa-${PKGVERSION}.tar.xz"
 
 mee_configure() {
     start_cmd ${S}/autogen.sh ${DEFCONFIG} \
+        --enable-autotools \
         --enable-gles1 \
         --enable-gles2 \
         --enable-osmesa \