* mk/targets.mk(GITVERSION): Provide commit number for shallow clones

Fall back to using git describe --always when git describe fails in
Org repo.

See https://orgmode.org/list/87bkmve8qv.fsf@gmail.com

mk/targets.mk

@@ -14,7 +14,7 @@ ifneq ($(wildcard .git),)
   # Use the org.el header.
   ORGVERSION := $(patsubst %-dev,%,$(shell $(BATCH) --eval "(require 'lisp-mnt)" \
     --visit lisp/org.el --eval '(princ (lm-header "version"))'))
-  GITVERSION ?= $(shell git describe --match release\* --abbrev=6 HEAD)
+  GITVERSION ?= $(shell git describe --match release\* --abbrev=6 HEAD 2>/dev/null || echo  "release_N/A-N/A-$(shell git describe --match release\* --abbrev=6 --always HEAD)")
   GITSTATUS  ?= $(shell git status -uno --porcelain)
 else
  -include mk/version.mk