openssh build failure on High Sierra (10.13.2)

[Zube]

Back in January/March of 2017, it was the case that building openssh
with the latest openssl on MacOS 10.12.x (Sierra) was a bit of
a bother.

I could build everything with Xcode, but the resulting sshd segfaulted
upon invocation (see the archives).  So I built gcc 6.3 and used that
to build openssh 7.x on Sierra.  As long as machines stayed on 10.12.x,
all was fine.

Under High Sierra, the Xcode behavior is the same, but the old gcc
6.3 compiler or a newly-built-under-High-Sierra gcc 6.4 fails to
build openssh 7.6p1 (or the latest SNAP) with:

/usr/local/gcc-6.3.0/bin/gcc -g -O2 -pipe -Wall
-Wpointer-arith -Wuninitialized -Wsign-compare -Wformat-security
-Wsizeof-pointer-memaccess -Wno-pointer-sign -Wno-unused-result
-fno-strict-aliasing -D_FORTIFY_SOURCE=2 -ftrapv -fno-builtin-memset
-fstack-protector-strong   -I. -I. -I/usr/local/sshssl102n/include
-DSSHDIR=\"/usr/local/ssh/etc\"
-D_PATH_SSH_PROGRAM=\"/usr/local/ssh/bin/ssh\"
-D_PATH_SSH_ASKPASS_DEFAULT=\"/usr/local/ssh/libexec/ssh-askpass\"
-D_PATH_SFTP_SERVER=\"/usr/local/ssh/libexec/sftp-server\"
-D_PATH_SSH_KEY_SIGN=\"/usr/local/ssh/libexec/ssh-keysign\"
-D_PATH_SSH_PKCS11_HELPER=\"/usr/local/ssh/libexec/ssh-pkcs11-helper\"
-D_PATH_SSH_PIDDIR=\"/var/run\"
-D_PATH_PRIVSEP_CHROOT_DIR=\"/var/empty\" -DHAVE_CONFIG_H -c log.c
-o log.o In file included from /usr/include/sys/cdefs.h:587:0,
                 from /usr/include/sys/types.h:75, from includes.h:25,
                 from log.c:37:
/usr/include/sys/syslog.h:227:124: error: expected ',' or ';' before
'__asm'
 void syslog(int, const char *, ...) __printflike(2, 3)
 __not_tail_called __DARWIN_ALIAS_STARTING(__MAC_10_13, __IPHONE_NA,
 __DARWIN_EXTSN(syslog));

The corresponding bits from syslog.h are [lines wrapped]

#if defined(__ENVIRONMENT_MAC_OS_X_VERSION_MIN_REQUIRED__) &&
__DARWIN_C_LEVEL >= __DARWIN_C_FULL

void    syslog(int, const char *, ...) __printflike(2, 3)
__not_tail_called __DARWIN_ALIAS_STARTING(__MAC_10_13, __IPHONE_NA,
__DARWIN_EXTSN(syslog));

#else
void    syslog(int, const char *, ...) __printflike(2, 3) __not_tail_called;
#endif

Any help is greatly appreciated.

Cheers,
Zube