为什么glGenVertexArray是为C程序定义的，而不是在Linux上的C ++程序？

请考虑以下文件：

#include <SDL.h>
#include <GLES2/gl2.h>

int main() {
    SDL_Init(SDL_INIT_VIDEO);
    SDL_Window *window = SDL_CreateWindow("Test", 0, 0, 200, 200, SDL_WINDOW_OPENGL | SDL_WINDOW_SHOWN);
    SDL_GLContext context = SDL_GL_CreateContext(window);
    GLuint vao;
    glGenVertexArrays(1, &vao);
}

如果上面的是test.c，那么下面的行代码）完美地工作：

If the above is test.c, then the following line (compiling as C code) works perfectly:

gcc test.c -I/usr/include/SDL2 -lGLESv2 -lSDL2

但是，下一个（编译为C ++代码）不会：

This next one (compiling as C++ code), however, does not:

gcc -x c++ test.c -I/usr/include/SDL2 -lGLESv2 -lSDL2

我得到的错误是：

test.c: In function ‘int main()’:
test.c:9:27: error: ‘glGenVertexArrays’ was not declared in this scope
  glGenVertexArrays(1, &vao);

我在x86 Linux上使用gcc 4.8.2编译，使用SDL 2.0和OpenGL ES 2.0。

I am compiling this on x86 Linux with gcc 4.8.2, using SDL 2.0 and OpenGL ES 2.0.

发生了什么事？许多其他OpenGL ES 2.0调用（glDrawArrays，glGenBuffers等）与C和C ++完美配合。另外，是不是C ++应该能够调用C库，特别是系统的（应该）设计来防止函数名称破坏？

What is going on? Many of the other OpenGL ES 2.0 calls that I make (glDrawArrays, glGenBuffers, etc.) work perfectly well with both C and C++. Additionally, isn't C++ supposed to be able to call C libraries, especially system ones that (should) be designed to prevent function name mangling?

什么是错误，如何解决此问题？

What is wrong, and how can I fix this?