improve checking for ldap.h and ldap_ssl.h header files

configure.ac

@@ -544,7 +544,24 @@ AC_HELP_STRING([--with-lber-lib=libname],[Specify name of lber lib file]),
 
 if test x$CURL_DISABLE_LDAP != x1 ; then
 
-  AC_CHECK_HEADERS(ldap.h)
+  AC_CHECK_HEADERS(lber.h)
+
+  AC_CHECK_HEADERS(ldap.h,
+    [],[],[
+#if HAVE_LBER_H
+#include <lber.h>
+#endif
+])
+
+  AC_CHECK_HEADERS(ldap_ssl.h,
+    [],[],[
+#if HAVE_LBER_H
+#include <lber.h>
+#endif
+#if HAVE_LDAP_H
+#include <ldap.h>
+#endif
+])
 
   if test -z "$LDAPLIBNAME" ; then
     case $host in
@@ -572,8 +589,6 @@ fi
 
 if test x$CURL_DISABLE_LDAP != x1 ; then
 
-  AC_CHECK_HEADERS(lber.h)
-
   if test "$LBERLIBNAME" ; then
     dnl If name is "no" then don't define this library at all
     dnl (it's only needed if libldap.so's dependencies are broken).
@@ -1768,7 +1783,6 @@ AC_CHECK_HEADERS(
         assert.h \
         unistd.h \
         stdlib.h \
-        ldap_ssl.h \
         limits.h \
         arpa/inet.h \
         net/if.h \