bug#43683: make install-exec does not trigger make $(BUILT_SOURCES)

[Karl Berry]

Hi madmurphy,

    install-exec: $(BUILT_SOURCES)
            $(MAKE) $(AM_MAKEFLAGS) install-exec-am

Thanks very much for the bug report, patch, and test case. I just
applied and pushed it, with small modifications. Please report back if
problems persist. Meanwhile, closing this bug. Thanks again! --karl