emacs: dump in postinst script with portable dumper

packages/emacs/Makefile.patch

@@ -0,0 +1,11 @@
+--- ../Makefile.in.orig	2020-09-14 22:21:34.172699093 +0200
++++ ./Makefile.in	2020-09-15 21:43:19.212824716 +0200
+@@ -365,7 +365,7 @@
+ 	  sed < ${srcdir}/src/epaths.in > epaths.h.$$$$		\
+ 	  -e 's;\(#.*PATH_LOADSEARCH\).*$$;\1 "${standardlisppath}";' \
+ 	  -e 's;\(#.*PATH_SITELOADSEARCH\).*$$;\1 "${locallisppath}";' \
+-	  -e 's;\(#.*PATH_DUMPLOADSEARCH\).*$$;\1 "${buildlisppath}";' \
++	  -e 's;\(#.*PATH_DUMPLOADSEARCH\).*$$;\1 "${standardlisppath}";' \
+ 	  -e '/^#define PATH_[^ ]*SEARCH /s/\([":]\):*/\1/g'		\
+ 	  -e '/^#define PATH_[^ ]*SEARCH /s/:"/"/'			\
+ 	  -e 's;\(#.*PATH_EXEC\).*$$;\1 "${archlibdir}";'		\

packages/emacs/build.sh

@@ -24,6 +24,8 @@ TERMUX_PKG_EXTRA_CONFIGURE_ARGS="
 --without-dbus
 --without-selinux
 --with-modules
+--with-pdumper=yes
+--with-dumping=none
 "
 # Ensure use of system malloc:
 TERMUX_PKG_EXTRA_CONFIGURE_ARGS+=" emacs_cv_sanitize_address=yes"
@@ -75,11 +77,6 @@ termux_step_post_get_source() {
 	# Termux only use info pages for emacs. Remove the info directory
 	# to get a clean Info directory file dir.
 	rm -Rf $TERMUX_PREFIX/share/info
-
-	# We cannot run a dumped emacs on Android 5.0+ due to the pie requirement.
-	# Also, the native emacs we build (bootstrap-emacs) cannot used dumps when
-	# building inside docker: https://github.com/docker/docker/issues/22801
-	export CANNOT_DUMP=yes
 }
 
 termux_step_host_build() {
@@ -115,6 +112,10 @@ termux_step_create_debscripts() {
 				$TERMUX_PREFIX/bin/editor editor $TERMUX_PREFIX/bin/emacs 40
 		fi
 	fi
+
+	cd $TERMUX_PREFIX/share/emacs/$TERMUX_PKG_VERSION/lisp
+	LC_ALL=C $TERMUX_PREFIX/bin/emacs -batch -l loadup --temacs=pdump
+	mv $TERMUX_PREFIX/bin/emacs*.pdmp $TERMUX_PREFIX/libexec/emacs/$TERMUX_PKG_VERSION/${TERMUX_ARCH}-linux-android*/
 	EOF
 
 	cat <<- EOF > ./prerm