pihpsdr: Doesn't use MacPorts LDFLAGS

[ryandesign (Ryan Carsten Schmidt)]

pihpsdr fails to build on 10.6 because although it includes the legacysupport portgroup it evidently doesn't use MacPorts LDFLAGS so it still fails to link with the legacysupport library which would have provided getline and clock_gettime:

​https://build.macports.org/builders/ports-10.6_x86_64-builder/builds/33611/steps/install-port/logs/stdio

/opt/local/bin/clang-mp-9.0 -o pihpsdr MacOS.o audio.o portaudio.o band.o configure.o discovered.o discovery.o filter.o version.o main.o new_menu.o about_menu.o rx_menu.o exit_menu.o radio_menu.o ant_menu.o display_menu.o dsp_menu.o pa_menu.o cw_menu.o oc_menu.o xvtr_menu.o equalizer_menu.o step_menu.o meter_menu.o band_menu.o bandstack_menu.o mode_menu.o filter_menu.o noise_menu.o agc_menu.o vox_menu.o fft_menu.o diversity_menu.o tx_menu.o vfo_menu.o test_menu.o meter.o mode.o old_discovery.o new_discovery.o old_protocol.o new_protocol.o new_protocol_programmer.o rx_panadapter.o tx_panadapter.o property.o radio.o receiver.o rigctl.o rigctl_menu.o toolbar.o transmitter.o zoompan.o sliders.o vfo.o waterfall.o button_text.o vox.o update.o store.o store_menu.o memory.o led.o ext.o error_handler.o cwramp.o protocols.o   \
		 iambic.o ps_menu.o \
		mac_midi.o midi2.o midi3.o stemlab_discovery.o -lm -lwdsp -lpthread -lportaudio  `pkg-config --libs gtk+-3.0`  `pkg-config --libs libcurl` -framework CoreMIDI -framework Foundation
Undefined symbols for architecture x86_64:
  "_strnlen", referenced from:
      _discovery in discovery.o
      _tcp_cb in discovery.o
  "_clock_gettime", referenced from:
      _programmer_thread in new_protocol_programmer.o
      _keyer_thread in iambic.o
      _NewMidiEvent in midi2.o
ld: symbol(s) not found for architecture x86_64

[Davide Gerhard <ra1nb0w@…>]

In 671a189aee1905fad93e376d41130f2546dd5cbf/macports-ports (master):

pihpsdr: update commit to 5bcbc75f

Closes: #61121