MFH: r518116

Use clang 7 as compiler on 11.x and 12.x to fix build.

clang 8 and later error for duplicate definitions of enum values.  mdb
depends on having identical but duplicate definitions.  This was fixed
differently in 13 with a change to the kernel, but that change is
disruptive and cannot be easily backported.

Reported by:	pkg-fallout, Attila Nagy
Approved by:	bdrewery
Differential Revision:	https://reviews.freebsd.org/D22486

Approved by:	ports-secteam (joneum)

devel/mdb/Makefile

@@ -9,7 +9,7 @@ COMMENT=	Solaris Modular Debugger
 
 LICENSE=	CDDL
 
-USES=		uidfix
+USES=		compiler uidfix
 
 USE_GITHUB=	yes
 GH_ACCOUNT=	bsdjhb
@@ -31,6 +31,15 @@ CFLAGS+=	-DMDB_PREFIX=\\\"${PREFIX}\\\" -g
 IGNORE=		requires full source tree with CDDL sources
 .endif
 
+.if ${OSVERSION} < 1300015 && ${COMPILER_TYPE} == "clang" && \
+    ${COMPILER_VERSION} >= 80
+# clang 8 cannot compile due to enum redefinitions in kernel.h
+BUILD_DEPENDS+=	${LOCALBASE}/bin/clang70:devel/llvm70
+CPP=	${LOCALBASE}/bin/clang-cpp70
+CC=	${LOCALBASE}/bin/clang70
+CXX=	${LOCALBASE}/bin/clang++70
+.endif
+
 pre-install:
 	${MKDIR} ${STAGEDIR}${PREFIX}/lib/mdb/kvm/${MACHINE_ARCH}