Thanks to Toke Høiland-Jørgensen <toke@toke.dk> for reporting this bug.
INSTALL_PROGRAM=@INSTALL_PROGRAM@
INSTALL_DATA=@INSTALL_DATA@
-git-label:=$(strip $(shell git describe --always --dirty=-x 2>/dev/null))
-ifneq ($(git-label),)
- CFLAGS += -DGIT_LABEL="$(git-label)"
-endif
-
client=$(addprefix $(exedir)/,@CLIENT@)
daemon=$(exedir)/bird
protocols=@protocols@
objdir := @objdir@
exedir := @exedir@
+git-label:=$(strip $(shell cd $(srcdir) && [ "$$(git rev-parse --show-toplevel)" = "$$(readlink -f .)" ] && git describe --always --dirty=-x 2>/dev/null))
+ifneq ($(git-label),)
+ CFLAGS += -DGIT_LABEL="$(git-label)"
+endif
+
ifeq ($(objdir),.)
objdir := $(realpath .)
endif