Reland Implement _ExtInt as an extended int type specifier.

I fixed the LLDB issue, so re-applying the patch.

This reverts commit a4b88c044980337bb14390be654fe76864aa60ec.
diff --git a/clang/lib/Serialization/ASTReader.cpp b/clang/lib/Serialization/ASTReader.cpp
index f0e9bbd..62dd233 100644
--- a/clang/lib/Serialization/ASTReader.cpp
+++ b/clang/lib/Serialization/ASTReader.cpp
@@ -6719,6 +6719,15 @@
   TL.setKWLoc(readSourceLocation());
 }
 
+void TypeLocReader::VisitExtIntTypeLoc(clang::ExtIntTypeLoc TL) {
+  TL.setNameLoc(readSourceLocation());
+}
+void TypeLocReader::VisitDependentExtIntTypeLoc(
+    clang::DependentExtIntTypeLoc TL) {
+  TL.setNameLoc(readSourceLocation());
+}
+
+
 void ASTRecordReader::readTypeLoc(TypeLoc TL) {
   TypeLocReader TLR(*this);
   for (; !TL.isNull(); TL = TL.getNextTypeLoc())