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/ParseTentative.cpp b/clang/lib/Parse/ParseTentative.cpp
index d6684c3..48393d9 100644
--- a/clang/lib/Parse/ParseTentative.cpp
+++ b/clang/lib/Parse/ParseTentative.cpp
@@ -1026,6 +1026,7 @@
   case tok::kw_char:
   case tok::kw_const:
   case tok::kw_double:
+  case tok::kw__Float16:
   case tok::kw___float128:
   case tok::kw_enum:
   case tok::kw_half:
@@ -1510,6 +1511,7 @@
   case tok::kw_half:
   case tok::kw_float:
   case tok::kw_double:
+  case tok::kw__Float16:
   case tok::kw___float128:
   case tok::kw_void:
   case tok::annot_decltype:
@@ -1600,6 +1602,7 @@
   case tok::kw_half:
   case tok::kw_float:
   case tok::kw_double:
+  case tok::kw__Float16:
   case tok::kw___float128:
   case tok::kw_void:
   case tok::kw___unknown_anytype: