maint: make position of gnulib checkout configurable

Some gnulib-related tools (most prominently, the gnulib-provided
'bootstrap' script) allow the user to define the position of his
gnulib's repository checkout through the use of the 'GNULIB_SRCDIR'
environment variable.  We should do the same, for consistency and
to easily support slightly unusual layouts in developers' source
trees.

* cfg.mk (gnulib_dir): Define to "$GNULIB_SRCDIR" if that's set,
and to default value of "'$(abs_srcdir)'/../gnulib" otherwise.
Update comments.

1 files changed, 5 insertions, 3 deletions

diff --git a/cfg.mk b/cfg.mk
index 6eb2fa44..a66c247c 100644
--- a/cfg.mk
+++ b/cfg.mk
@@ -26,9 +26,11 @@ _autoreconf = autoreconf -i -v && rm -f INSTALL
 # Used in maint.mk's web-manual rule
 manual_title = Creating Automatic Configuration Scripts
 
-# The local directory containing the checked-out copy of gnulib used in this
-# release (override the default).
-gnulib_dir = '$(abs_srcdir)'/../gnulib
+# The local directory containing the checked-out copy of gnulib used
+# in this release (override the default).  The $GNULIB_SRCDIR variable
+# is also honored by the gnulib-provided bootstrap script, so using it
+# here is consistent.
+gnulib_dir = $${GNULIB_SRCDIR-'$(abs_srcdir)'/../gnulib}
 
 # The bootstrap tools (override the default).
 bootstrap-tools = automake