Vulkan: Fix point coord management

The gl_PointCoord.y coordinate needs to be flipped
around the X axis in Vulkan to have correct results.

Bug: angleproject:2457

Change-Id: I0d87ad28366623c2be0867c610cc35678a4af43f
Reviewed-on: https://chromium-review.googlesource.com/1090824
Reviewed-by: Luc Ferron <lucferron@chromium.org>
Reviewed-by: Olli Etuaho <oetuaho@nvidia.com>
Commit-Queue: Luc Ferron <lucferron@chromium.org>
diff --git a/src/compiler/translator/util.cpp b/src/compiler/translator/util.cpp
index a7f0465..ceeb1ba 100644
--- a/src/compiler/translator/util.cpp
+++ b/src/compiler/translator/util.cpp
@@ -641,6 +641,15 @@
     }
 }
 
+void DeclareGlobalVariable(TIntermBlock *root, const TVariable *variable)
+{
+    TIntermDeclaration *declaration = new TIntermDeclaration();
+    declaration->appendDeclarator(new TIntermSymbol(variable));
+
+    TIntermSequence *globalSequence = root->getSequence();
+    globalSequence->insert(globalSequence->begin(), declaration);
+}
+
 // GLSL ES 1.0.17 4.6.1 The Invariant Qualifier
 bool CanBeInvariantESSL1(TQualifier qualifier)
 {