(e.g., Interix) still expect a shlib to be executable, and INSTALL_DATA installs with mode 644 (non-executable).
not build a shared library on platforms that libtool thinks can't handle inter-library dependencies, e.g. OpenBSD and Solaris.
<URL:http://mail.gnu.org/pipermail/bug-gnu-utils/2002-September/002920.html>.