lang/ghc: Use correct LLVM toolchain for the bootstrap compiler.

PR:		264192
Reported by:	Mark Millard <marklmi26-fbsd@yahoo.com>

lang/ghc/Makefile

@@ -40,7 +40,7 @@ GMP_DESC=		Use GNU Multi-precision Library from Ports
 PROFILE_DESC=		Add support for performance profiling
 
 BOOT_CONFIGURE_ENV=	GHC=${LOCALBASE}/bin/ghc
-BOOT_CONFIGURE_ENV_OFF=	GHC=${BOOT_GHC}
+BOOT_CONFIGURE_ENV_OFF=	GHC=${BOOT_GHC} LLC=llc${BOOT_LLVM_VERSION} OPT=opt${BOOT_LLVM_VERSION}
 
 DOCS_BUILD_DEPENDS=	sphinx-build:textproc/py-sphinx
 DOCS_VARS=		enable_docs=YES