mesa-demos: only install useful tools

The cleanup code is taken from a SlackBuild (see for instance:
https://ftp.slackware.pl/pub/slackware/slackware64-current/source/x/mesa/mesa.SlackBuild)

This shredds over 300 completely useless files like:

/usr/bin/arbocclude2
/usr/bin/pixeltest
/usr/bin/quad-clip-nearplane
/usr/bin/vp-tri-imm
/usr/share/mesa-demos/girl2.rgb

mesa-demos.be0

@@ -61,10 +61,23 @@ SRCURL[0]="https://mesa.freedesktop.org/archive/demos/mesa-demos-${PKGVERSION}.t
 #    bee_build
 #}
 
-#mee_install() {
-#    bee_install
-#}
-## by default this may be 'make install DESTDIR="${D}"'
+# Install all the demos (including the pointless ones) at first, in a
+# temporary location:
+mee_install() {
+    start_cmd make install DESTDIR=${D}/cruft
+}
+
+# Install gears and glinfo, as well as a few other demos:
+mee_install_post() {
+    mkdir -p ${D}/usr/bin
+    for demo in gears glinfo glthreads glxcontexts glxdemo glxgears \
+      glxgears_fbconfig glxheads glxinfo glxpbdemo glxpixmap ; do
+      mv --verbose ${D}/cruft/usr/bin/$demo ${D}/usr/bin
+    done
+    # Remove cruft:
+    rm -rf ${D}/cruft
+}
+
 
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