[LLDB][NFC] Add the mojo language to Language::GetPrimaryLanguage

This doesn't change the current behavior of the function, but the explicit declaration looks cleaner.

lldb/source/Target/Language.cpp

@@ -374,6 +374,7 @@ LanguageType Language::GetPrimaryLanguage(LanguageType language) {
   case eLanguageTypeJulia:
   case eLanguageTypeDylan:
   case eLanguageTypeMipsAssembler:
+  case eLanguageTypeMojo:
   case eLanguageTypeUnknown:
   default:
     return language;