message: fix gcc compiler error about for loop initial declaration
diff: @@ -64,7 +64,8 @@ void mySkeletonCallback(void *userdata, const OSVR_TimeValue *timestamp,
  printf("\tnumJoints: %d, numBones: %d\n", numJoints, numBones);
  - for (OSVR_SkeletonJointCount joint = 0; joint < numJoints; joint++) {
  + OSVR_SkeletonJointCount joint;
  + for (joint = 0; joint < numJoints; joint++) {
  uint32_t len = 0;
  OSVR_SkeletonJointCount jointId = 0;
  rc = osvrClientGetSkeletonAvailableJointId(skel, joint, &jointId);
  @@ -112,7 +113,8 @@ void mySkeletonCallback(void *userdata, const OSVR_TimeValue *timestamp,
  osvrQuatGetW(&jointState.pose.rotation));
  }
  - for (OSVR_SkeletonBoneCount bone = 0; bone < numBones; bone++) {
  + OSVR_SkeletonBoneCount bone;
  + for (bone = 0; bone < numBones; bone++) {
  uint32_t len = 0;
  OSVR_SkeletonBoneCount boneId = 0;
  rc = osvrClientGetSkeletonAvailableBoneId(skel, bone, &boneId);
  