Basic/Diagnostics: Add an isDefaultMappingAsError method, and switch TextDiagnosticPrinter to use that instead of extracting the current mapping via getDiagnosticLevel, which fixes one class of corner cases w.r.t. printing the "-Werror" diagnostic option marker.
 - The TextDiagnosticPrinter code is still fragile as it is just "reverse engineering" what the diagnostic engine is doing. Not my current priority to fix though.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@140752 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/test/Frontend/diagnostics-option-names.c b/test/Frontend/diagnostics-option-names.c
new file mode 100644
index 0000000..ed0d2ed
--- /dev/null
+++ b/test/Frontend/diagnostics-option-names.c
@@ -0,0 +1,8 @@
+// RUN: not %clang_cc1 -fdiagnostics-show-option -Werror -Weverything %s 2> %t
+// RUN: FileCheck < %t %s
+
+int f0(int, unsigned);
+int f0(int x, unsigned y) {
+// CHECK: comparison of integers of different signs{{.*}} [-Werror,-Wsign-compare]
+  return x < y; // expected-error {{ : 'int' and 'unsigned int'  }}
+}