Atomic shared library install permissions on HP-UX.

Atomic shared library install permissions on HP-UX.

The HP-UX 11 runtime linker fails to mmap shared libraries
without execute permissions.  Fixing them with postinstall_cmds
may be too late, as ln, sed, and chmod may link against the
library being installed.

* libltdl/m4/libtool.m4 (install_override_mode): New LT_DECL.
(_LT_SYS_DYNAMIC_LINKER) [hpux9*, hpux10*, hpux11*]: Set it.
* libltdl/config/ltmain.m4sh (func_mode_install): Build a second
command line, $install_shared_prog, for the installation of the
shared library.  Override resp. set the permission mode if
install_override_mode is nonempty.
* doc/libtool.texi (libtool script contents): Document it.
* tests/install.at (Install tests): New test.
* Makefile.am (TESTSUITE_AT): Adjust.
(TESTS_ENVIRONMENT): Pass INSTALL.
Report by Bruno Haible.

Signed-off-by: Ralf Wildenhues <Ralf.Wildenhues@gmx.de>