Switch to clang-r407598 (12.0.1).

Also suppress a clang-tidy warning and a ubsan check to pass compilation.

Bug: 171348143
Test: build.
Change-Id: Ie5162c15df172cefd7cff9776e54531fd620bc23

cc/config/clang.go

@@ -94,6 +94,7 @@ var ClangLibToolingUnknownCflags = sorted([]string{})
 // `modernize-*`.
 var ClangTidyDisableChecks = []string{
 	"misc-no-recursion",
+	"readability-function-cognitive-complexity", // http://b/175055536
 }
 
 func init() {
@@ -190,6 +191,8 @@ func init() {
 		"-Wno-pessimizing-move",                     // http://b/154270751
 		// New warnings to be fixed after clang-r399163
 		"-Wno-non-c-typedef-for-linkage", // http://b/161304145
+		// New warnings to be fixed after clang-r407598
+		"-Wno-string-concatenation", // http://b/175068488
 	}, " "))
 
 	// Extra cflags for external third-party projects to disable warnings that