databases/mongodb70: fix build on 14-CURRENT

Port does not build with clang15 but does with clang14.

/usr/include/c++/v1/__algorithm/comp.h:36:71: error: invalid operands to binary expression ('const mongo::SSLX509Name::Entry' and 'const mongo::SSLX509Name::Entry')
    bool operator()(const _T1& __x, const _T1& __y) const {return __x == __y;}
                                                                  ~~~ ^  ~~~

databases/mongodb70/Makefile

@@ -1,6 +1,7 @@
 PORTNAME=	mongodb
 DISTVERSIONPREFIX=	r
 DISTVERSION=	7.0.0-rc0
+PORTREVISION=	1
 CATEGORIES=	databases net
 PKGNAMESUFFIX=	${DISTVERSION:R:S/.//}
 
@@ -52,6 +53,7 @@ python_OLD_CMD=	@python_interpreter@
 MAKE_ARGS=	--cxx-std=20 \
 		--disable-warnings-as-errors \
 		--libc++ \
+		--allocator=system \
 		--runtime-hardening=on \
 		--use-system-libunwind \
 		--use-system-pcre2 \
@@ -87,6 +89,14 @@ SSL_MAKE_ARGS=	--ssl
 
 .include <bsd.port.pre.mk>
 
+# MongoDB 7.0 fails on clang15.
+.if ${CHOSEN_COMPILER_TYPE} == clang && ${OPSYS} == FreeBSD && ${OSVERSION} >= 1400079
+_LLVM_VERSION=  14
+BUILD_DEPENDS+= clang${_LLVM_VERSION}:devel/llvm${_LLVM_VERSION}
+CC=             ${LOCALBASE}/bin/clang${_LLVM_VERSION}
+CXX=            ${LOCALBASE}/bin/clang++${_LLVM_VERSION}
+.endif
+
 ALL_TARGET=	install-core
 
 # This ports is only following the Major Release.