+#
+# Do these checks ONLY if we're re-building the "configure"
+# scripts, and ONLY the "configure" scripts. If we leave
+# these rules enabled by default, then they're run too often.
+#
+ifeq "$(MAKECMDGOALS)" "reconfig"
+
+CONFIGURE_AC_FILES := $(shell find . -name configure.ac -print)
+CONFIGURE_FILES := $(patsubst %.ac,%,$(CONFIGURE_AC_FILES))
+
+#
+# The GNU tools make autoconf=="missing autoconf", which then returns
+# 0, even when autoconf doesn't exist. This check is to ensure that
+# we run AUTOCONF only when it exists.
+#
+AUTOCONF_EXISTS := $(shell autoconf --version 2>/dev/null)
+
+ifeq "$(AUTOCONF_EXISTS)" ""
+$(error You need to install autoconf to re-build the "configure" scripts)
+endif