make[3]: Entering directory `/home/desrt/jhbuild/checkout/gupnp-igd/tests/examples'
  CCLD   test
  CCLD   test-thread
test-thread.o: In function `main':
/home/desrt/jhbuild/checkout/gupnp-igd/tests/examples/test-thread.c:52: undefined reference to `g_thread_init'
collect2: error: ld returned 1 exit status
test.o: In function `main':
/home/desrt/jhbuild/checkout/gupnp-igd/tests/examples/test.c:67: undefined reference to `g_thread_init'
collect2: error: ld returned 1 exit status



Either a) stop calling g_thread_init() [it is deprecated]

or b) explicitly add gthread-2.0 to your pkgconfig checks in configure.ac


The long story here is that many modules (specifically libraries) have stopped calling g_thread_init() and therefore have dropped their dependency on the gthread-2.0 pkgconfig.  One of them was probably implicitly pulling it in for you as a dependency before, but is no longer.