Add implementation of SPV_EXT_fragment_fully_covered

This implementation uses the GLSL extension
GL_NV_conservative_raster_underestimation to generate the new SPIR-V
FullyCoveredEXT built in.

SPIRV/GLSL.ext.EXT.h

@@ -0,0 +1,39 @@
+/*
+** Copyright (c) 2014-2016 The Khronos Group Inc.
+**
+** Permission is hereby granted, free of charge, to any person obtaining a copy
+** of this software and/or associated documentation files (the "Materials"),
+** to deal in the Materials without restriction, including without limitation
+** the rights to use, copy, modify, merge, publish, distribute, sublicense,
+** and/or sell copies of the Materials, and to permit persons to whom the
+** Materials are furnished to do so, subject to the following conditions:
+**
+** The above copyright notice and this permission notice shall be included in
+** all copies or substantial portions of the Materials.
+**
+** MODIFICATIONS TO THIS FILE MAY MEAN IT NO LONGER ACCURATELY REFLECTS KHRONOS
+** STANDARDS. THE UNMODIFIED, NORMATIVE VERSIONS OF KHRONOS SPECIFICATIONS AND
+** HEADER INFORMATION ARE LOCATED AT https://www.khronos.org/registry/
+**
+** THE MATERIALS ARE PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS
+** OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+** FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL
+** THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+** LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
+** FROM,OUT OF OR IN CONNECTION WITH THE MATERIALS OR THE USE OR OTHER DEALINGS
+** IN THE MATERIALS.
+*/
+
+#ifndef GLSLextEXT_H
+#define GLSLextEXT_H
+
+enum BuiltIn;
+enum Op;
+enum Capability;
+
+static const int GLSLextEXTVersion = 100;
+static const int GLSLextEXTRevision = 1;
+
+static const char* const E_SPV_EXT_fragment_fully_covered = "SPV_EXT_fragment_fully_covered";
+
+#endif  // #ifndef GLSLextEXT_H