For me the C-down-mouse-1 solution worked, but still used the point from before the click. Thus I use now:

(define-key c-mode-base-map [C-down-mouse-1] 'mouse-drag-region)
(define-key c-mode-base-map [C-mouse-1] 'rtags-find-symbol-at-point)

so now, first the point gets set, then we find the correct symbol.

For me the C-down-mouse-1 solution worked, but still used the point from before the click. Thus I use now:

(define-key c-mode-base-map [C-down-mouse-1] 'mouse-drag-region)
(define-key c-mode-base-map [C-mouse-1] 'rtags-find-symbol-at-point)

so now, first the point gets set, then we find the correct symbol.