Improve the ltdl discovery code by checking for libtool 2.x functions.

The lt_dladvise_* interfaces are implemented only in the 2.x series and are
not implemented in 1.4, so we can rely on their presence to know that the
version is good enough.

diff --git a/configure.ac b/configure.ac
index 11f98764cfb209a4941cdc539c985d75732908df..bc6c1ce669ef5eeeb64e679ffbe03ca0a14c2046 100644 (file)
--- a/configure.ac
+++ b/configure.ac
@@ -244,6 +244,10 @@ dnl exactly which version of libltdl is present in the system, so we
 dnl just assume that it's a working version as long as we have the
 dnl library and the header files.
 dnl
+dnl As an extra safety device, check for lt_dladvise_init() which is
+dnl only implemented in libtool 2.x, and refine as we go if we have
+dnl refined requirements.
+dnl
 dnl Check the header files first since the system may have a
 dnl libltdl.so for runtime, but no headers, and we want to bail out as
 dnl soon as possible.
@@ -253,7 +257,7 @@ dnl can give the proper place to find libltdl through the standard
 dnl variables like LDFLAGS and CPPFLAGS.
 
 AC_CHECK_HEADER([ltdl.h],
-    [AC_CHECK_LIB([ltdl], [lt_dlopen], [LIBLTDL=-lltdl], [LIBLTDL=])],
+    [AC_CHECK_LIB([ltdl], [lt_dladvise_init], [LIBLTDL=-lltdl], [LIBLTDL=])],
     [LIBLTDL=])
 
 AS_IF([test "x$LIBLTDL" = "x"],