avsprintf(): Fix a bug in usage of va_list on x86. On x86, va_list is a...

avsprintf():  Fix a bug in usage of va_list on x86.  On x86, va_list is a pointer to a single copy on the stack.  avsprintf() calls lib_vsprintf() twice and so traverses the va_list twice using va_start.  va_start modifies that single copy on the stack so that the second call to lib_vsprintf() fails.  This appears to be an issue with x86 only so far