In Non-Project Mode, read each file individually before executing the compilation commands.
The example script below shows how to use one or more XDC files for synthesis and implementation.
Example Script:
read_verilog [glob src/*.v]
read_xdc wave_gen_timing.xdc
read_xdc wave_gen_pins.xdc
synth_design -top wave_gen -part xc7k325tffg900-2
opt_design
place_design
route_design