raise an exception on dirseek, thus to allow us compilation.
bionic libc does now support wide characters.
we cannot run compiled code when cross_compiling.
i manually compiled socket extensions tests and run them on a
device running the bionic libc.
then i hardcoded results by looking at the RUBY_PLATFORM variable.
fd_set is defined into <sys/select.h> on bionic libc.
do not assume to HAVE_LANGINFO_H on bionic libc.