libtool: fix sys_lib_dlsearch_path_spec for ia64 HP-UX.

The run-time loader does not search /usr/local or subdirectories
by default on ia64 HP-UX.
* m4/libtool.m4 (_LT_SYS_DYNAMIC_LINKER): Fix
sys_lib_dlsearch_path_spec for ia64 HP-UX.
* NEWS: Update.

Signed-off-by: Gary V. Vaughan <gary@gnu.org>