Compilation will not work if the header is missing, so make sure
it is present and compilable first. This can highligh sooner if
a user forgot to install the corresponding dev package.
Signed-off-by: Christophe CURIS <christophe.curis@free.fr>
Took the opportunity to rewrite the check using autoconf macros
to generate a more compatible configure script.
Signed-off-by: Christophe CURIS <christophe.curis@free.fr>