Catch some buildsystem errors

[ndim]

This catches some errors which can happen in the build system:

• If autoreconf fails for some reason (exit with code != 0), there is no good reason for the autogen.sh script to succeed.(exit with code 0).

• If the system does not have libtool installed, the LT_INIT m4 macro is not available and therefore the configure script cannot be generated properly. This should result in autoreconf aborting with an error, and not in the configure script containing a line of verbatim LT_INIT([disable-static win32-dll pic-only]). m4_pattern_forbid provides just that.

JFTR, I stumbled upon this due to https://stackoverflow.com/questions/73355119/error-libtool-library-used-but-libtool-is-undefined-but-libtool-installed-on.

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[stephane]

Thank you @ndim. No need CLA for minor changes (even more when there are not in source code). Merged.