configure.in : Modification done by Michel Jouvin to fix a problem with

configure.in : Modification done by Michel Jouvin to fix a problem with
library search path on Tru64.

According to autoconf maintainer suggestion, move -L/path/to/lib from LIBS
variable to LDFLAGS. This was done because on some systems (like Tru64)
-Lpath must appear before -llib that requires  -L. This is not the case
if -L is in LIBS as -l are inserted at the head of LIBS by autoconf to
preserve library search order required by some systems.