glslang preprocessing: Add -E option to print out preprocessed GLSL, and do the work needed to generate a preprocessed stream. From Andrew Woloszyn <awoloszyn@google.com>.

git-svn-id: https://cvs.khronos.org/svn/repos/ogl/trunk/ecosystem/public/sdk/tools/glslang@31508 e7fa87d3-cd2b-0410-9028-fcbf551c1848

Test/preprocessor.pragma.vert

@@ -0,0 +1,11 @@
+#version 310 es
+
+#pragma optimize(on)
+#pragma optimize(off)
+#pragma debug(on)
+#pragma debug(off)
+
+#pragma undefined_pragma(x, 4)
+
+int main() {
+}