wlfreerdp: fix compilation errors

This commit fixes the following errors:
wlfreerdp.c:(.text.startup+0xc): undefined reference to
`freerdp_channels_global_init'
wlfreerdp.c:(.text.startup+0x72): undefined reference to
`freerdp_client_parse_command_line_arguments'
wlfreerdp.c:(.text.startup+0x9b): undefined reference to
`freerdp_channels_global_uninit'