Issue #15819: use standard autoconf preset output variables.
Reported by: Roumen Petrov
diff --git a/configure b/configure
index a619bb3..6e1825f 100755
--- a/configure
+++ b/configure
@@ -715,7 +715,6 @@
HGTAG
HGVERSION
BASECPPFLAGS
-BUILDDIR
target_alias
host_alias
build_alias
@@ -2721,10 +2720,8 @@
-BUILDDIR="`pwd`"
-
-if test "$srcdir" != "." -a "$srcdir" != "$BUILDDIR"; then
+if test "$abs_srcdir" != "$abs_builddir"; then
# If we're building out-of-tree, we need to make sure the following
# resources get picked up before their $srcdir counterparts.
# Objects/ -> typeslots.inc