glsl: Define GL_ES preprocessor macro if API is OpenGL ES 2.0.

Also define it if #version 100 is encountered.
diff --git a/src/glsl/main.cpp b/src/glsl/main.cpp
index 30f11a5..2323a20 100644
--- a/src/glsl/main.cpp
+++ b/src/glsl/main.cpp
@@ -130,7 +130,7 @@
 
    const char *source = shader->Source;
    state->error = preprocess(state, &source, &state->info_log,
-			     state->extensions);
+			     state->extensions, API_OPENGL);
 
    if (!state->error) {
       _mesa_glsl_lexer_ctor(state, source);