Bug 1345478 - Make the PrintErrorKind::Error case explicitly unreacha…

…ble in PrintSingleError; r=bbouvier

This patch explicitly calls MOZ_CRASH() in the switch case
PrintErrorKind::Error that is never reached inside the function
PrintSingleError in the file js/src/jscntxt.cpp.
Explicitly handling all the possible cases avoids the compiler to issue
warnings for them: a non handled case in the switch code that might derive
from additions to the enum class PrintErrorKind can be caught at compile time
rather then having a default switch case for handling it, which instead would
be called at runtime.

MozReview-Commit-ID: ECZlMoLvn2m

UltraBlame original commit: 1741441028b5e0713da9d93f175c0f8c79e87749

js/src/jscntxt.cpp

@@ -552,7 +552,7 @@ PrintSingleError(JSContext* cx, FILE* file, JS::ConstUTF8CharsZ toStringResult,
         const char* kindPrefix = nullptr;
         switch (kind) {
           case PrintErrorKind::Error:
-            break;
+            MOZ_CRASH("unreachable");
           case PrintErrorKind::Warning:
             kindPrefix = "warning";
             break;