Fix clang 18.1.6

Fix all syntax errors reported by clang++ version 18.1.6.

testsuite/mbdyn_build_job.sh

@@ -44,7 +44,9 @@ if ! test -f "${program_dir}/mbdyn_build_job.sh"; then
     program_dir=$(realpath $(which "${program_name}"))
 fi
 
-LIBDIR64="${LIBDIR64:-lib lib64}" ## FIXME: On some systems it is called "lib64" whereas it is called "lib" on other systems.
+## FIXME: On some systems it is called "lib64" whereas it is called "lib" on other systems.
+## FIXME: In any case "lib64" should take precedence over "lib".
+LIBDIR64="${LIBDIR64:-lib64 lib}"
 MBD_SOURCE_DIR=${MBD_SOURCE_DIR:-`dirname ${program_dir}`}
 MBD_SKIP_BUILD="${MBD_SKIP_BUILD:-no}"
 MBD_INSTALL_PREFIX="${MBD_INSTALL_PREFIX:-${program_dir}/var/cache/mbdyn}"
@@ -304,7 +306,9 @@ if test -d "${SICONOS_INSTALL_PREFIX}"; then
         fi
     done
     CPPFLAGS="-I${SICONOS_INC_DIR} ${CPPFLAGS}"
-    LDFLAGS="-L${SICONOS_LIB_DIR} -Wl,-rpath=${SICONOS_LIB_DIR} ${LDFLAGS}"
+    if ! test -z "${SICONOS_LIB_DIR}"; then
+        LDFLAGS="-L${SICONOS_LIB_DIR} -Wl,-rpath=${SICONOS_LIB_DIR} ${LDFLAGS}"
+    fi
 fi
 
 echo "Detecting NetCDF ..."