mesa: Fix const correctness of API implementation functions.

This patch changes the use of const in the type signatures of
_mesa_ShaderSource() and _mesa_TransformFeedbackVaryings(), to match
the type signatures in the GL spec.  This avoids warnings when
building the code-generated api_exec.c file.

Note: previously we avoided the build warnings because these functions
were being type-checked against ShaderSourceARB and
TransformFeedbackVaryingsEXT; those functions are semantically
equivalent, but have fewer const qualifiers in their type signatures.

Acked-by: Brian Paul <brianp@vmware.com>

src/mesa/main/shaderapi.c

@@ -1292,7 +1292,7 @@ read_shader(const char *fname)
  */
 void GLAPIENTRY
 _mesa_ShaderSource(GLhandleARB shaderObj, GLsizei count,
-                      const GLcharARB ** string, const GLint * length)
+                      const GLcharARB * const * string, const GLint * length)
 {
    GET_CURRENT_CONTEXT(ctx);
    GLint *offsets;

src/mesa/main/shaderapi.h

@@ -112,7 +112,7 @@ extern void GLAPIENTRY
 _mesa_LinkProgram(GLhandleARB programObj);
 
 extern void GLAPIENTRY
-_mesa_ShaderSource(GLhandleARB, GLsizei, const GLcharARB* *, const GLint *);
+_mesa_ShaderSource(GLhandleARB, GLsizei, const GLcharARB* const *, const GLint *);
 
 extern void GLAPIENTRY
 _mesa_UseProgram(GLhandleARB);

src/mesa/main/transformfeedback.c

@@ -512,7 +512,8 @@ _mesa_BindBufferOffsetEXT(GLenum target, GLuint index, GLuint buffer,
  */
 void GLAPIENTRY
 _mesa_TransformFeedbackVaryings(GLuint program, GLsizei count,
-                                const GLchar **varyings, GLenum bufferMode)
+                                const GLchar * const *varyings,
+                                GLenum bufferMode)
 {
    struct gl_shader_program *shProg;
    GLint i;

src/mesa/main/transformfeedback.h

@@ -73,7 +73,8 @@ _mesa_BindBufferOffsetEXT(GLenum target, GLuint index, GLuint buffer,
 
 extern void GLAPIENTRY
 _mesa_TransformFeedbackVaryings(GLuint program, GLsizei count,
-                                const GLchar **varyings, GLenum bufferMode);
+                                const GLchar * const *varyings,
+                                GLenum bufferMode);
 
 extern void GLAPIENTRY
 _mesa_GetTransformFeedbackVarying(GLuint program, GLuint index,