debian: compile executable with PIE

This patch fixes hardening-no-pie lintian warning. Ubuntu Xenial uses
older versions of gcc which not build ELF binaries with PIE by default,
but since Xenial builds did not trigger this warning, we do not change
the behavior with additional flags.

Part of #5372, closes #6390

debian/rules

@@ -28,7 +28,7 @@ DEB_DH_SYSTEMD_START_ARGS_tarantool-common  := --no-restart-on-upgrade tarantool
 
 # Needed for proper backtraces in fiber.info()
 DEB_DH_STRIP_ARGS	        := -X/usr/bin/tarantool
-export DEB_BUILD_MAINT_OPTIONS = hardening=-stackprotector,-pie
+export DEB_BUILD_MAINT_OPTIONS = hardening=-stackprotector
 DPKG_EXPORT_BUILDFLAGS = 1
 
 include /usr/share/dpkg/buildflags.mk