[MSan] add KMSAN support to Clang driver

Boilerplate code for using KMSAN instrumentation in Clang.

We add a new command line flag, -fsanitize=kernel-memory, with a
corresponding SanitizerKind::KernelMemory, which, along with
SanitizerKind::Memory, maps to the memory_sanitizer feature.

KMSAN is only supported on x86_64 Linux.

It's incompatible with other sanitizers, but supports code coverage
instrumentation.

llvm-svn: 341641
diff --git a/clang/test/Driver/fsanitize-coverage.c b/clang/test/Driver/fsanitize-coverage.c
index ab8b1c6..acc712c 100644
--- a/clang/test/Driver/fsanitize-coverage.c
+++ b/clang/test/Driver/fsanitize-coverage.c
@@ -9,6 +9,7 @@
 // RUN: %clang -target x86_64-linux-gnu -fsanitize=hwaddress -fsanitize-coverage=func,trace-pc %s -### 2>&1 | FileCheck %s --check-prefix=CHECK-SANITIZE-COVERAGE-FUNC
 // RUN: %clang -target x86_64-linux-gnu -fsanitize=kernel-hwaddress -fsanitize-coverage=func,trace-pc %s -### 2>&1 | FileCheck %s --check-prefix=CHECK-SANITIZE-COVERAGE-FUNC
 // RUN: %clang -target x86_64-linux-gnu -fsanitize=memory -fsanitize-coverage=func,trace-pc %s -### 2>&1 | FileCheck %s --check-prefix=CHECK-SANITIZE-COVERAGE-FUNC
+// RUN: %clang -target x86_64-linux-gnu -fsanitize=kernel-memory -fsanitize-coverage=func,trace-pc %s -### 2>&1 | FileCheck %s --check-prefix=CHECK-SANITIZE-COVERAGE-FUNC
 // RUN: %clang -target x86_64-linux-gnu -fsanitize=leak -fsanitize-coverage=func,trace-pc %s -### 2>&1 | FileCheck %s --check-prefix=CHECK-SANITIZE-COVERAGE-FUNC
 // RUN: %clang -target x86_64-linux-gnu -fsanitize=undefined -fsanitize-coverage=func,trace-pc %s -### 2>&1 | FileCheck %s --check-prefix=CHECK-SANITIZE-COVERAGE-FUNC
 // RUN: %clang -target x86_64-linux-gnu -fsanitize=bool -fsanitize-coverage=func,trace-pc %s -### 2>&1 | FileCheck %s --check-prefix=CHECK-SANITIZE-COVERAGE-FUNC