Extend FindTypes with CompilerContext to allow filtering by language.

This patch is also motivated by the Swift branch and is effectively NFC for the single-TypeSystem llvm.org branch.

In multi-language projects it is extremely common to have, e.g., a
Clang type and a similarly-named rendition of that same type in
another language. When searching for a type It is much cheaper to pass
a set of supported languages to the SymbolFile than having it
materialize every result and then rejecting the materialized types
that have the wrong language.

Differential Revision: https://reviews.llvm.org/D66546

<rdar://problem/54471165>

This reapplies r369690 with a previously missing constructor for LanguageSet.

llvm-svn: 369710
diff --git a/lldb/source/Target/Language.cpp b/lldb/source/Target/Language.cpp
index 3c3ef28..43d0be0 100644
--- a/lldb/source/Target/Language.cpp
+++ b/lldb/source/Target/Language.cpp
@@ -357,26 +357,16 @@
   return supported_languages;
 }
 
-void Language::GetLanguagesSupportingTypeSystems(
-    std::set<lldb::LanguageType> &languages,
-    std::set<lldb::LanguageType> &languages_for_expressions) {
-  uint32_t idx = 0;
-
-  while (TypeSystemEnumerateSupportedLanguages enumerate = PluginManager::
-             GetTypeSystemEnumerateSupportedLanguagesCallbackAtIndex(idx++)) {
-    (*enumerate)(languages, languages_for_expressions);
-  }
+LanguageSet Language::GetLanguagesSupportingTypeSystems() {
+  return PluginManager::GetAllTypeSystemSupportedLanguagesForTypes();
 }
 
-void Language::GetLanguagesSupportingREPLs(
-    std::set<lldb::LanguageType> &languages) {
-  uint32_t idx = 0;
+LanguageSet Language::GetLanguagesSupportingTypeSystemsForExpressions() {
+  return PluginManager::GetAllTypeSystemSupportedLanguagesForExpressions();
+}
 
-  while (REPLEnumerateSupportedLanguages enumerate =
-             PluginManager::GetREPLEnumerateSupportedLanguagesCallbackAtIndex(
-                 idx++)) {
-    (*enumerate)(languages);
-  }
+LanguageSet Language::GetLanguagesSupportingREPLs() {
+  return PluginManager::GetREPLAllTypeSystemSupportedLanguages();
 }
 
 std::unique_ptr<Language::TypeScavenger> Language::GetTypeScavenger() {