compiler can't tell int from function? nmh-1.0.4

[Dieter]

FreeBSD 6.0-RELEASE
AMD64
compiling port nmh-1.0.4

cc -c -DHAVE_CONFIG_H -I.. -I. -I.. -O2 -fno-strict-aliasing -pipe  -DFLOCK_LOCKING context_read.c
In file included from ../h/mh.h:337,
                 from context_read.c:8:
../h/prototypes.h:73: warning: function declaration isn't a prototype
context_read.c:12: warning: function declaration isn't a prototype


    10  #include <pwd.h>
    11
    12  extern int errno;    <-- doesn't look like a function to me?
    13
    14  void
    15  context_read (void)
    16  {

I also have -Wmissing-declarations -Wmissing-prototypes -Wstrict-prototypes
-Wpointer-arith -Wimplicit -Wreturn-type -Wformat -static turned on.

Am I missing something or is the compiler out to lunch?