mk: Put the version number somewhere discoverable in the installer

The binaries for some release channels to not contain the version number,
which makes it hard for scripts to determine the version number.

mk/dist.mk

@@ -212,7 +212,7 @@ distcheck-osx: dist-osx
 # Unix binary installer tarballs
 ######################################################################
 
-NON_INSTALLED_PREFIXES=COPYRIGHT,LICENSE-APACHE,LICENSE-MIT,README.md
+NON_INSTALLED_PREFIXES=COPYRIGHT,LICENSE-APACHE,LICENSE-MIT,README.md,version
 
 define DEF_INSTALLER
 
@@ -236,6 +236,8 @@ dist-install-dir-$(1): prepare-base-dir-$(1) docs compiler-docs
 	$$(Q)$$(PREPARE_MAN_CMD) $$(S)LICENSE-APACHE $$(PREPARE_DEST_DIR)/share/doc/rust
 	$$(Q)$$(PREPARE_MAN_CMD) $$(S)LICENSE-MIT $$(PREPARE_DEST_DIR)/share/doc/rust
 	$$(Q)$$(PREPARE_MAN_CMD) $$(S)README.md $$(PREPARE_DEST_DIR)/share/doc/rust
+# This tiny morsel of metadata is used by rust-packaging
+	$$(Q)echo "$(CFG_VERSION)" > $$(PREPARE_DEST_DIR)/version
 
 dist/$$(PKG_NAME)-$(1).tar.gz: dist-install-dir-$(1)
 	@$(call E, build: $$@)