Simplify autoconf checks by using AC_CHECK_FUNCS/HEADERS.
Clarify some ambiguous dependencies around strnlen/strndup.
Unconditionally enable pidwraptest for all arc4random implementations.
Remove HAVE_VASPRINTF conditional, since asprintf requires vasprintf.
ok @doug
it seems that including stdarg.h is needed for defining va_list
environment is hpux 11.31(ia64) with gcc 4.7.1.
without stdarg.h, I got compilation error like this.
"error: 'va_list' undeclared (first use in this function)"
I checked with gcc -E, then I noticed that __va_list is defined but va_list is not.
"typedef __gnuc_va_list __va_list;"
with including stdarg.h, va_list is defined.
"typedef __gnuc_va_list va_list;"
