[ASan] Initial support for Kernel AddressSanitizer

This patch adds initial support for the -fsanitize=kernel-address flag to Clang.
Right now it's quite restricted: only out-of-line instrumentation is supported, globals are not instrumented, some GCC kasan flags are not supported.
Using this patch I am able to build and boot the KASan tree with LLVMLinux patches from github.com/ramosian-glider/kasan/tree/kasan_llvmlinux.
To disable KASan instrumentation for a certain function attribute((no_sanitize("kernel-address"))) can be used.

llvm-svn: 240131

clang/lib/CodeGen/CodeGenModule.cpp

@@ -1218,8 +1218,9 @@ bool CodeGenModule::isInSanitizerBlacklist(llvm::Function *Fn,
 bool CodeGenModule::isInSanitizerBlacklist(llvm::GlobalVariable *GV,
                                            SourceLocation Loc, QualType Ty,
                                            StringRef Category) const {
-  // For now globals can be blacklisted only in ASan.
-  if (!LangOpts.Sanitize.has(SanitizerKind::Address))
+  // For now globals can be blacklisted only in ASan and KASan.
+  if (!LangOpts.Sanitize.hasOneOf(
+          SanitizerKind::Address | SanitizerKind::KernelAddress))
     return false;
   const auto &SanitizerBL = getContext().getSanitizerBlacklist();
   if (SanitizerBL.isBlacklistedGlobal(GV->getName(), Category))