maint: absolute VPATH build fix

[Akim Demaille]

Hi all,

Another tiny fix for VPATH builds.

commit 84901ee087f54dfa3db4b7c7dd5d2bb4deccb97c
Author: Akim Demaille <address@hidden>
Date:   Sat Jul 28 12:40:53 2012 +0200

    maint: absolute VPATH build fix
    
    * top/maint.mk (gpg_key_ID): Use -C to help git find .git when, for
    instance, $(srcdir) is not a parent of $(builddir).

diff --git a/top/maint.mk b/top/maint.mk
index baff0e9..8d504b9 100644
--- a/top/maint.mk
+++ b/top/maint.mk
@@ -1257,7 +1257,7 @@ bootstrap-tools ?= autoconf,automake,gnulib
 # If it's not already specified, derive the GPG key ID from
 # the signed tag we've just applied to mark this release.
 gpg_key_ID ?= \
-  $$(git cat-file tag v$(VERSION) \
+  $$(git -C $(srcdir) cat-file tag v$(VERSION) \
      | gpgv --status-fd 1 --keyring /dev/null - - 2>/dev/null \
      | awk '/^\[GNUPG:\] ERRSIG / {print $$3; exit}')