Integrated change #18270 from the perl core, which fixed a problem
in which xsubpp can make nested comments in C code (which is
bad). [Nicholas Clark]When no "MODULE ... PACKAGE ... PREFIX" line is found, it's now
still a fatal error for ParseXS, but we exit with status 0, which
is what the old xsubpp did and seems to work best with some modules
like Win32::NetAdmin. See RT ticket 11472. [Steve Hay]