ka9q-radio fails to build with glibc < 2.34

libpthread was integrated into glibc in version 2.34 (released August 2021). As a result, it is no longer necessary to explicitly link to it with -lpthread.

In e410528e, -lpthread was removed, which means that ka9q-radio no longer builds with earlier glibc versions:

cc  -o aprs aprs.o libradio.a -lbsd -lm
/usr/bin/ld: libradio.a(misc.o): in function `realtime':
misc.c:(.text+0x249): undefined reference to `pthread_getname_np'
/usr/bin/ld: misc.c:(.text+0x298): undefined reference to `pthread_getname_np'
/usr/bin/ld: libradio.a(misc.o): in function `norealtime':
misc.c:(.text+0x3be): undefined reference to `pthread_getname_np'
/usr/bin/ld: misc.c:(.text+0x430): undefined reference to `pthread_getname_np'
collect2: error: ld returned 1 exit status
make: *** [Makefile.linux:122: aprs] Error 1

Thus older OSes like Debian 11 and Ubuntu 20.04 are no longer supported.

Was this change intentional? If not, then -lpthread should be added back for programs that need it. It may also be worth extending CI to build ka9q-radio on multiple OS versions to catch accidental breakage of this sort.