Disable _glewSearchExtension for GLEW_OSMESA mode, it's not needed

auto/src/glew_head.c

@@ -178,6 +178,7 @@ static GLuint _glewStrCopy(char *d, const char *s, char c)
   return i;
 }
 
+#if !defined(GLEW_OSMESA)
 #if !defined(__APPLE__) || defined(GLEW_APPLE_GLX)
 static GLboolean _glewStrSame (const GLubyte* a, const GLubyte* b, GLuint n)
 {
@@ -188,6 +189,7 @@ static GLboolean _glewStrSame (const GLubyte* a, const GLubyte* b, GLuint n)
   return i == n ? GL_TRUE : GL_FALSE;
 }
 #endif
+#endif
 
 static GLboolean _glewStrSame1 (const GLubyte** a, GLuint* na, const GLubyte* b, GLuint nb)
 {
@@ -248,6 +250,7 @@ static GLboolean _glewStrSame3 (const GLubyte** a, GLuint* na, const GLubyte* b,
  * other extension names. Could use strtok() but the constant
  * string returned by glGetString might be in read-only memory.
  */
+#if !defined(GLEW_OSMESA)
 #if !defined(__APPLE__) || defined(GLEW_APPLE_GLX)
 static GLboolean _glewSearchExtension (const char* name, const GLubyte *start, const GLubyte *end)
 {
@@ -263,3 +266,4 @@ static GLboolean _glewSearchExtension (const char* name, const GLubyte *start, c
   return GL_FALSE;
 }
 #endif
+#endif