glx: Avoid atof() when computing the server's GLX version

atof() is locale-dependent (sigh), which means 1.3 becomes 1.0 if the
locale's decimal separator isn't a full-stop. Just use the protocol
major/minor instead. This would be slightly broken if the server
generically implements 1.3+ but a particular screen is only capable of
less, but in practice no such servers exist.

Gitlab: https://gitlab.freedesktop.org/mesa/mesa/issues/74
Reviewed-by: Eric Engestrom <eric.engestrom@intel.com>

src/glx/glxext.c

@@ -714,7 +714,8 @@ static GLboolean
    LockDisplay(dpy);
 
    psc->configs = NULL;
-   if (atof(priv->serverGLXversion) >= 1.3) {
+   if (priv->majorVersion > 1 ||
+       (priv->majorVersion == 1 && priv->minorVersion >= 3)) {
       GetReq(GLXGetFBConfigs, fb_req);
       fb_req->reqType = priv->majorOpcode;
       fb_req->glxCode = X_GLXGetFBConfigs;