[fetchmail]fetchmail build failure on tru64 5.1 + compaq c compiler

Hello all --

I'm having a hell of a time trying to build fetchmail 5.9.11 on
Tru64 UNIX with the vendor's C compiler (which has never given me any
trouble before).  Is this a known issue?  Pertinent software versions:

  > cc -V
  Compaq C V6.3-025 on Compaq Tru64 UNIX V5.1 (Rev. 732)
  Compiler Driver V6.3-026 (sys) cc Driver

  > flex --version
  flex version 2.5.4

The most painless possible build (./configure --disable-nls) eventually
gives up on smtp.c.  Here's some sample output from just smtp.c:

--- begin build output ---
  cc -DHAVE_CONFIG_H  -DLOCALEDIR=\"/usr/local/share/locale\" -c  -I. -I. 
-I./intl -I./intl -DHESIOD -I/usr/local/include -O smtp.c
  cc: Warning: fetchmail.h, line 403: Invalid token discarded. (invaltoken)
      __attribute__ ((format (printf, 2, 3)))
  ----^
  cc: Warning: fetchmail.h, line 406: Invalid token discarded. (invaltoken)
      __attribute__ ((format (printf, 2, 3)))
  ----^
  cc: Warning: fetchmail.h, line 409: Invalid token discarded. (invaltoken)
      __attribute__ ((format (printf, 2, 3)))
  ----^
  cc: Warning: fetchmail.h, line 412: Invalid token discarded. (invaltoken)
      __attribute__ ((format (printf, 5, 6)))
  ----^
  cc: Warning: fetchmail.h, line 435: Invalid token discarded. (invaltoken)
      __attribute__ ((format (printf, 2, 3)))
  ----^
  cc: Warning: fetchmail.h, line 439: Invalid token discarded. (invaltoken)
      __attribute__ ((format (printf, 2, 3)))
  ----^
  cc: Warning: fetchmail.h, line 491: Invalid token discarded. (invaltoken)
      __attribute__ ((format (printf, 2, 3)))
  ----^
  cc: Error: smtp.c, line 65: Missing ";".  This condition may have been caused 
by an open brace without a matching close brace.  The compiler will attempt to 
identify open braces that might be missing a close brace. (nosemi1)
          {
  --------^
  cc: Warning: smtp.c, line 62: This open brace may be missing a close brace 
and causing the syntax error at line number 65 in file smtp.c. (badopenbrace)
  {
  ^
  cc: Error: smtp.c, line 76: Invalid declarator. (declarator)
          if (!username || !password) return;
  --------^
  cc: Error: smtp.c, line 122: Invalid declarator. (declarator)
          else if (strstr(buf, "PLAIN")) {
  --------^
  cc: Error: smtp.c, line 143: Invalid declarator. (declarator)
          else if (strstr(buf, "LOGIN")) {
  --------^
  cc: Error: smtp.c, line 180: Invalid declarator. (declarator)
          return;
  --------^
  cc: Warning: smtp.c, line 64: The block-level declaration of the function 
"SMTP_auth_error" specifies an explicit storage class other than extern. 
(funcstrcls)
          static void SMTP_auth_error(int sock, char *msg)
  --------------------^
  cc: Error: smtp.c, line 68: In this statement, "msg" is not declared. 
(undeclared)
                  if (outlevel >= O_MONITOR) report(stdout, msg);
  ----------------------------------------------------------^
  make: *** [smtp.o] Error 1
--- end build output ---

I've been scratching my head about the obvious lines in fetchmail.h:

  #if !defined __GNUC__ || __GNUC__ < 2
  # define __attribute__(xyz)<BB>    /* Ignore. */
  #endif

But I've not come to any conclusion otherwise.  Any ideas?

Thanks,
Scott