debian: Build reproducibly

debian/rules

@@ -2,6 +2,13 @@
 
 export CARGO_HOME = $(CURDIR)/debian/cargo
 export DEB_BUILD_MAINT_OPTIONS = hardening=+all
+# Don't use paths that may change between builds.
+# No need to care about $HOME
+# because Cargo will not place any source in ~/.cargo.
+# The build directory is a subdirectory of the source directory,
+# so it doesn't need to be explicitly taken care of.
+export RUSTFLAGS = --remap-path-prefix=$(CURDIR)=/remap-pwd
+
 
 distrel := $(shell lsb_release --codename --short)
 ifneq (,$(filter $(distrel),buster amber))