Add pthread link annotations in lib bindings

[straight-shoota]

In older versions of glibc (< 2.34), pthread is a separate library and needs to be explicitly added as linker argument.

This implicitly works with programs that use the garbage collector, because a link annotation is added there to ensure proper link order:

crystal/src/gc/boehm.cr

Lines 16 to 17 in ef05e26

	# OTHERS: On other systems, we add the linker annotation here to make sure libpthread is loaded
	# before libgc which looks up symbols from libpthread.

But when using -Dgc_none we were missing link annotations for pthread since the cleanup in #11563

This patch adds the missing annotation to the glibc bindings for pthread symbols. Other platforms might be affected as well (BSDs?), but it's only confirmed to be an issue for GNU so far.

Resolves #11986