Teach the MSVC toolchain driver to link the correct asan libraries.

Now that the static runtime is gone the required librares are different.

Note that /MD or -D_DLL causes the dynamic runtime to get linked,
this is a little gross but emulates the behavior of MSVC.

"Real" msvc will link the debug build of asan if you specify /DEBUG or _DEBUG,
but that's not really necessary and requires building multiple
configurations from the same tree.

Author: barcharcraz

clang/lib/Driver/ToolChains/MSVC.cpp

@@ -196,10 +196,10 @@ void visualstudio::Linker::ConstructJob(Compilation &C, const JobAction &JA,
   if (TC.getSanitizerArgs(Args).needsAsanRt()) {
     CmdArgs.push_back(Args.MakeArgString("-debug"));
     CmdArgs.push_back(Args.MakeArgString("-incremental:no"));
-    if (TC.getSanitizerArgs(Args).needsSharedRt() ||
-        Args.hasArg(options::OPT__SLASH_MD, options::OPT__SLASH_MDd)) {
-      for (const auto &Lib : {"asan_dynamic", "asan_dynamic_runtime_thunk"})
-        CmdArgs.push_back(TC.getCompilerRTArgString(Args, Lib));
+    CmdArgs.push_back(TC.getCompilerRTArgString(Args, "asan_dynamic"));
+    auto defines = Args.getAllArgValues(options::OPT_D);
+    if (Args.hasArg(options::OPT__SLASH_MD, options::OPT__SLASH_MDd) ||
+        find(begin(defines), end(defines), "_DLL") != end(defines)) {
       // Make sure the dynamic runtime thunk is not optimized out at link time
       // to ensure proper SEH handling.
       CmdArgs.push_back(Args.MakeArgString(
@@ -208,19 +208,15 @@ void visualstudio::Linker::ConstructJob(Compilation &C, const JobAction &JA,
               : "-include:__asan_seh_interceptor"));
       // Make sure the linker consider all object files from the dynamic runtime
       // thunk.
-      CmdArgs.push_back(Args.MakeArgString(std::string("-wholearchive:") +
+      CmdArgs.push_back(Args.MakeArgString(
+          std::string("-wholearchive:") +
           TC.getCompilerRT(Args, "asan_dynamic_runtime_thunk")));
-    } else if (DLL) {
-      CmdArgs.push_back(TC.getCompilerRTArgString(Args, "asan_dll_thunk"));
     } else {
-      for (const auto &Lib : {"asan", "asan_cxx"}) {
-        CmdArgs.push_back(TC.getCompilerRTArgString(Args, Lib));
-        // Make sure the linker consider all object files from the static lib.
-        // This is necessary because instrumented dlls need access to all the
-        // interface exported by the static lib in the main executable.
-        CmdArgs.push_back(Args.MakeArgString(std::string("-wholearchive:") +
-            TC.getCompilerRT(Args, Lib)));
-      }
+      // Make sure the linker consider all object files from the static runtime
+      // thunk.
+      CmdArgs.push_back(Args.MakeArgString(
+          std::string("-wholearchive:") +
+          TC.getCompilerRT(Args, "asan_static_runtime_thunk")));
     }
   }