Enable GL_OES_standard_derivatives extension

Enable GL_OES_standard_derivatives extension
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i want to enable GL_OES_standard_derivatives for my shader in order to have more functions which I need for the following:

const char* ccPositionColorLengthTexture_frag = R"(

#ifdef GL_ES
 #extension GL_OES_standard_derivatives : enable

varying mediump vec4 v_color;
varying mediump vec2 v_texcoord;
varying vec4 v_color;
varying vec2 v_texcoord;

void main()
 #if defined GL_OES_standard_derivatives
 gl_FragColor = v_color*smoothstep(0.0, length(fwidth(v_texcoord)), 1.0 - length(v_texcoord));
    gl_FragColor = v_color*step(0.0, 1.0 - length(v_texcoord));

I got the following error:

ERROR: 0:22: ‘’ : syntax error: #extension must always be before any
non-preprocessor tokens

If I comment out the #extension line and just have this code:

gl_FragColor = v_color*smoothstep(0.0, length(fwidth(v_texcoord)), 1.0 - length(v_texcoord));

I got:

Invalid call of undeclared identifier ‘fwidth’

In the CCGlprogramm.h I found the following comment:

Create or Initializes the GLProgram with a vertex and fragment with
bytes array, with shader headers definition(eg. #version … or #extension …), with compileTimeDefines(eg. #define …).

static GLProgram* createWithByteArrays(const GLchar* vShaderByteArray, const GLchar* fShaderByteArray, const std::string& compileTimeHeaders, const std::string& compileTimeDefines);

I also tried to add the #extension line in the predefined headers in the bool GLProgram::compileShader function like so:

    if (compileTimeHeaders.empty()) {
        headersDef = (type == GL_VERTEX_SHADER ? "precision mediump float;\n precision mediump int;\n" : "precision mediump float;\n precision mediump int;\n");
        headersDef = (type == GL_VERTEX_SHADER ? "precision highp float;\n precision highp int;\n" : "#extension GL_OES_standard_derivatives : enable;\n precision mediump float;\n precision mediump int;\n");
        headersDef = compileTimeHeaders;

The following error appears:

cocos2d: ERROR: 0:1: ‘’ : syntax error: #extension

I want to enable the GL_OES_standard_derivatives cause it seems like the solution for the antialiasing problem of the DrawNode. I found this which is more or less the same for Cocos2d-Iphone.

Can someone give me an advice here.