snprintf in opensmtpd

OpenSMTPD has been configured with the following options:
                     User binaries: /usr/local/bin
                   System binaries: /usr/local/sbin
               Configuration files: /usr/local/etc
                mail.local program: /usr/local/libexec/opensmtpd/mail.local
                   encrypt program: /usr/local/libexec/opensmtpd/encrypt
                      Manual pages: /usr/local/share/man/manX
                    smtpd.sock dir: /var/run
  Privilege separation chroot path: /var/empty
                    Manpage format: doc
                       PAM support: no
                  BSD Auth support: no

              Host: x86_64-apple-darwin15.3.0
          Compiler: gcc
    Compiler flags: -g -O2  -Qunused-arguments -Wunknown-warning-option -Wall -Wpointer-arith -Wuninitialized -Wsign-compare -Wformat-security -Wsizeof-pointer-memaccess -Wno-pointer-sign -Wno-unused-result -fno-strict-aliasing -fno-builtin-memset
Preprocessor flags: -I/Users/sme/pkg/include
      Linker flags: -L/Users/sme/pkg/lib
         Libraries: -lasr -levent -lcrypto -lssl -lresolv -lz
      DB Libraries:

1059 % make
/Applications/Xcode.app/Contents/Developer/usr/bin/make  all-recursive
Making all in openbsd-compat
gcc -DHAVE_CONFIG_H -I. -I..  -I../smtpd -I../openbsd-compat -I/Users/sme/pkg/include   -g -O2  -Qunused-arguments -Wunknown-warning-option -Wall -Wpointer-arith -Wuninitialized -Wsign-compare -Wformat-security -Wsizeof-pointer-memaccess -Wno-pointer-sign -Wno-unused-result -fno-strict-aliasing -fno-builtin-memset  -c -o arc4random.o arc4random.c
In file included from arc4random.c:27:
In file included from ./includes.h:77:
./openbsd-compat.h:152:5: warning: incompatible redeclaration of library function 'snprintf' [-Wincompatible-library-redeclaration]
int snprintf(char *, size_t, SNPRINTF_CONST char *, ...);
    ^
./openbsd-compat.h:152:5: note: 'snprintf' is a builtin with type 'int (char *, unsigned long, const char *, ...)'
1 warning generated.
gcc -DHAVE_CONFIG_H -I. -I..  -I../smtpd -I../openbsd-compat -I/Users/sme/pkg/include   -g -O2  -Qunused-arguments -Wunknown-warning-option -Wall -Wpointer-arith -Wuninitialized -Wsign-compare -Wformat-security -Wsizeof-pointer-memaccess -Wno-pointer-sign -Wno-unused-result -fno-strict-aliasing -fno-builtin-memset  -c -o base64.o base64.c
In file included from base64.c:47:
In file included from ./includes.h:77:
./openbsd-compat.h:152:5: warning: incompatible redeclaration of library function 'snprintf' [-Wincompatible-library-redeclaration]
int snprintf(char *, size_t, SNPRINTF_CONST char *, ...);
    ^
./openbsd-compat.h:152:5: note: 'snprintf' is a builtin with type 'int (char *, unsigned long, const char *, ...)'
In file included from base64.c:58:
/Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX10.11.sdk/usr/include/stdio.h:421:6: error:
      conflicting types for 'snprintf'
int      snprintf(char * __restrict, size_t, const char * __restrict, ...) __printflike(3, 4);
         ^
./openbsd-compat.h:152:5: note: previous declaration is here
int snprintf(char *, size_t, SNPRINTF_CONST char *, ...);
    ^
1 warning and 1 error generated.
make[2]: *** [base64.o] Error 1
make[1]: *** [all-recursive] Error 1
make: *** [all] Error 2