Fix GENERIC-KASAN kernel build for amd64

Work around llvm/llvm-project#87923, which
leads to an assertion failure compiling several kernel source files with
asan enabled.

PR:		276104
MFC after:	1 month

(cherry picked from commit b811dac)

Author: DimitryAndric

sys/conf/kern.pre.mk

@@ -111,6 +111,11 @@ SAN_CFLAGS+=	-DSAN_NEEDS_INTERCEPTORS -DSAN_INTERCEPTOR_PREFIX=kasan \
 #	upstreamed similar to: https://reviews.llvm.org/D98285
 #
 SAN_CFLAGS+=	-mllvm -asan-mapping-offset=0xdfff208000000000
+.elif ${MACHINE_CPUARCH} == "amd64" && \
+      ${COMPILER_TYPE} == "clang" && ${COMPILER_VERSION} >= 180000
+# Work around https://github.com/llvm/llvm-project/issues/87923, which leads to
+# an assertion failure compiling dtrace.c with asan enabled.
+SAN_CFLAGS+=	-mllvm -asan-use-stack-safety=0
 .endif
 .endif