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/baseResults/preprocessor.simple.vert.out

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+#version 310 es
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+             float fn(float x){ return x + 4.0;}
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+int main(){
+  gl_Position = vec4(1);
+  gl_Position = clamp(1, 2, 3);
+  gl_Position = vec4(1);
+  gl_Position = vec4(1, 2);
+  gl_Position = vec4(fn(3));
+}
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