merge from panda3d_1_8_branch: work around conflicting declarations of glShaderSource

panda/src/glstuff/glGraphicsStateGuardian_src.cxx

@@ -1042,7 +1042,7 @@ reset() {
        get_extension_func(GLPREFIX_QUOTED, "GetUniformLocation");
     _glLinkProgram = (PFNGLLINKPROGRAMPROC)
        get_extension_func(GLPREFIX_QUOTED, "LinkProgram");
-    _glShaderSource = (PFNGLSHADERSOURCEPROC)
+    _glShaderSource = (PFNGLSHADERSOURCEPROC_P)
        get_extension_func(GLPREFIX_QUOTED, "ShaderSource");
     _glUseProgram = (PFNGLUSEPROGRAMPROC)
        get_extension_func(GLPREFIX_QUOTED, "UseProgram");

panda/src/glstuff/glGraphicsStateGuardian_src.h

@@ -153,7 +153,7 @@ typedef void (APIENTRYP PFNGLGETSHADERIVPROC) (GLuint shader, GLenum pname, GLin
 typedef void (APIENTRYP PFNGLGETSHADERINFOLOGPROC) (GLuint shader, GLsizei bufSize, GLsizei *length, GLchar *infoLog);
 typedef GLint (APIENTRYP PFNGLGETUNIFORMLOCATIONPROC) (GLuint program, const GLchar *name);
 typedef void (APIENTRYP PFNGLLINKPROGRAMPROC) (GLuint program);
-typedef void (APIENTRYP PFNGLSHADERSOURCEPROC) (GLuint shader, GLsizei count, const GLchar **string, const GLint *length);
+typedef void (APIENTRYP PFNGLSHADERSOURCEPROC_P) (GLuint shader, GLsizei count, const GLchar* const *string, const GLint *length);
 typedef void (APIENTRYP PFNGLUSEPROGRAMPROC) (GLuint program);
 typedef void (APIENTRYP PFNGLUNIFORM4FPROC) (GLint location, GLfloat v0, GLfloat v1, GLfloat v2, GLfloat v3);
 typedef void (APIENTRYP PFNGLUNIFORM1IPROC) (GLint location, GLint v0);
@@ -664,7 +664,7 @@ public:
   PFNGLGETSHADERINFOLOGPROC _glGetShaderInfoLog;
   PFNGLGETUNIFORMLOCATIONPROC _glGetUniformLocation;
   PFNGLLINKPROGRAMPROC _glLinkProgram;
-  PFNGLSHADERSOURCEPROC _glShaderSource;
+  PFNGLSHADERSOURCEPROC_P _glShaderSource;
   PFNGLUSEPROGRAMPROC  _glUseProgram;
   PFNGLUNIFORM4FPROC _glUniform4f;
   PFNGLUNIFORM1IPROC _glUniform1i;