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.edge_cases.vert

@@ -0,0 +1,15 @@
+#version 310 es
+#define X(Y) /*
+                */ Y + 2
+
+#define Y(Z) 2 * Z// asdf
+
+#define Z(Y) /*
+                */ \
+  2 /*
+       */ + 3 \
+    * Y
+
+void main() {
+  gl_Position = vec4(X(3) + Y(4) + Z(2));
+}