out can't be used with non-varying FragColor

因为片段着色器缺少glsl的版本号，加上版本号就可以了

#version 330   //不能缺少

in vec2 TexCoord0;

out vec4 FragColor;

uniform sampler2D gSampler;

void main()
{
    FragColor = texture2D(gSampler, TexCoord0.st);
};