build-package.sh: introduce field "Pre-Depends"

Required in rare cases where package update may break package manager during
installation process.

See https://www.debian.org/doc/debian-policy/ch-relationships.html for
more information.

scripts/build/termux_step_create_debfile.sh

@@ -16,6 +16,7 @@ termux_step_create_debfile() {
 		Homepage: $TERMUX_PKG_HOMEPAGE
 	HERE
 	test ! -z "$TERMUX_PKG_BREAKS" && echo "Breaks: $TERMUX_PKG_BREAKS" >> DEBIAN/control
+	test ! -z "$TERMUX_PKG_PRE_DEPENDS" && echo "Pre-Depends: $TERMUX_PKG_PRE_DEPENDS" >> DEBIAN/control
 	test ! -z "$TERMUX_PKG_DEPENDS" && echo "Depends: $TERMUX_PKG_DEPENDS" >> DEBIAN/control
 	test ! -z "$TERMUX_PKG_ESSENTIAL" && echo "Essential: yes" >> DEBIAN/control
 	test ! -z "$TERMUX_PKG_CONFLICTS" && echo "Conflicts: $TERMUX_PKG_CONFLICTS" >> DEBIAN/control

scripts/build/termux_step_setup_variables.sh

@@ -90,6 +90,7 @@ termux_step_setup_variables() {
 	TERMUX_PKG_BUILD_IN_SRC=""
 	TERMUX_PKG_RM_AFTER_INSTALL=""
 	TERMUX_PKG_BREAKS="" # https://www.debian.org/doc/debian-policy/ch-relationships.html#s-binarydeps
+	TERMUX_PKG_PRE_DEPENDS=""
 	TERMUX_PKG_DEPENDS=""
 	TERMUX_PKG_BUILD_DEPENDS=""
 	TERMUX_PKG_HOMEPAGE=""