build: add new TARNAME variable

That expands to `@PACKAGE_TARNAME@`, similar to the existing
PACKAGE_TARNAME variable.

To make it easier to use (and read) and to be more consistent with the
surrounding variables (NAME and VERSION).

Note that the original PACKAGE_TARNAME is still needed, as by default
(on autoconf v2.69) `docdir=@docdir@` in config.mk.in expands to the
following in config.mk:

    docdir=${datarootdir}/doc/${PACKAGE_TARNAME}

1 files changed, 2 insertions, 1 deletions

diff --git a/config.mk.in b/config.mk.in
index 7eed050ca..9973b7eaa 100644
--- a/config.mk.in
+++ b/config.mk.in
@@ -8,7 +8,8 @@
 # first target encountered).
 
 NAME=@PACKAGE_NAME@
-PACKAGE_TARNAME=@PACKAGE_TARNAME@
+TARNAME=@PACKAGE_TARNAME@
+PACKAGE_TARNAME=@PACKAGE_TARNAME@ # needed by docdir
 VERSION=@PACKAGE_VERSION@
 
 prefix=@prefix@