[MacPorts] #37583: Update tcl.m4 macro in base to add a check for tcl8.6

#37583: Update tcl.m4 macro in base to add a check for tcl8.6 -------------------------+-------------------------------- Reporter: egall@… | Owner: macports-tickets@… Type: enhancement | Status: new Priority: Normal | Milestone: Component: base | Version: 2.1.2 Keywords: haspatch | Port: -------------------------+-------------------------------- Pretty simple patch, just adds a few lines, it's attached -- Ticket URL: <https://trac.macports.org/ticket/37583> MacPorts <http://www.macports.org/> Ports system for Mac OS