Recommit "Add _Float16 as a C/C++ source language type"

This is a recommit of r312781; in some build configurations
variable names are omitted, so changed the new regression
test accordingly.

llvm-svn: 312794
diff --git a/clang/lib/Parse/ParseExprCXX.cpp b/clang/lib/Parse/ParseExprCXX.cpp
index 6ef747f..cfe03d7 100644
--- a/clang/lib/Parse/ParseExprCXX.cpp
+++ b/clang/lib/Parse/ParseExprCXX.cpp
@@ -1928,6 +1928,9 @@
   case tok::kw_double:
     DS.SetTypeSpecType(DeclSpec::TST_double, Loc, PrevSpec, DiagID, Policy);
     break;
+  case tok::kw__Float16:
+    DS.SetTypeSpecType(DeclSpec::TST_float16, Loc, PrevSpec, DiagID, Policy);
+    break;
   case tok::kw___float128:
     DS.SetTypeSpecType(DeclSpec::TST_float128, Loc, PrevSpec, DiagID, Policy);
     break;