shaderlab: Matrix-vector multiplication in fragment shader on iOS not working?

I want to calculate screenspace normals and therefore try to performa a matrix-vector multiplication in the fragment shader. It works in the editor, but outputs pink on iOS.

this is my test fragment shader:

 half4 frag( v2f i ) : COLOR
 {
     return float4(0,1,0,0);
     //return mul(UNITY_MATRIX_MVP, float4(0,1,0,0));
 }

outputs as expected green. but when comment the first line and uncomment the second line instead, the shader fails. Xcode shows me the following output:

 Fragment Shader:
 precision mediump float;
 
 #define SHADER_API_GLES 1
 #define tex2D texture2D
 
 #define gl_ModelViewProjectionMatrix glstate_matrix_mvp
 uniform mat4 glstate_matrix_mvp;
 
 void main ()
 {
   mediump vec4 tmpvar_1;
   tmpvar_1 = (gl_ModelViewProjectionMatrix * vec4(0.00000, 1.00000, 0.00000, 0.00000));
   gl_FragData[0] = tmpvar_1;
 }
 
 Unsupported: MyShader

is this line the problem?

 #define SHADER_API_GLES 1

http://http.developer.nvidia.com/Cg/mul.html states that

 mul is supported in all profiles except the fp20, ps_1_1, ps_1_2, and ps_1_3 fragment profiles.

I'm not sure how that translates to GLES profiles, but I assume this could be the problem? how do I target GLES2 instead?