databases/mongodb60: mark ignore on FreeBSD 12.3.

Summary:
Llvm in FreeBSD 12.3 gives several compile errors.
One example:
src/mongo/s/sharding_initialization.cpp:171:49: error: no viable constructor or deduction guide for deduction of template arguments of 'weak_ptr'
    connPoolOptions.controllerFactory = [srwp = std::weak_ptr(srsp)] {

http://beefy6.nyi.freebsd.org/data/123amd64-default/0116f5c59197/logs/errors/mongodb60-6.0.2.log

12.4 is expected to work again due to new libc++

PR:	266587
Approved by: rene (mentor)
MFH:	2022Q4
Differential Revision: https://reviews.freebsd.org/D37230

databases/mongodb60/Makefile

@@ -87,6 +87,10 @@ SSL_MAKE_ARGS=	--ssl
 
 .include <bsd.port.pre.mk>
 
+.if ${OSREL} == "12.3"
+IGNORE=		does not compile on 12.3, libc++ too old
+.endif
+
 ALL_TARGET=	install-core
 
 # This ports is only following the Major Release.