configure: skip useless/harmful C++/F77 checks by libtool

AC_PROG_LIBTOOL configure macro wants to run a lot of C++ and Fortran checks
Since vzctl does not use any C++ or Fortran code, those checks are useless.

But this is not a problem -- the problem is in case of there is no C++
compiler, configure fails miserably with the following diagnostics:

  checking how to run the C++ preprocessor... /lib/cpp
  configure: error: C++ preprocessor "/lib/cpp" fails sanity check

So we have a strange situation -- inability to compile C code on a system
without C++ compiler. This is weird. The word is they have fixed it in
libtool-1.5.10, but still there is no ability to skip useless C++/F77 checks
in libtool 1.5.

The word is libtool 1.6 and newer has this fixed by introducing macro
AC_LIBTOOL_TAGS. If one put AC_LIBTOOL_TAGS([]) in configure.ac, those
checks will be skipped completely. Do not forget to use that in future.
For now, this dirty hack should suffice.
1 file changed