musl thread fix (#1)

* Deduplicate the cleanup in handle_connection()

* Remove the VLA from handle_connection()

This fixes a segfault on musl libc with reasonable sized buffers, as
musl's default thread stack size is quite small (128k since 1.1.21).

A similar bug exists on glibc with large enough buffers (reproducable
with e.g. 16MB on my test system).

This commit fixes solusipse#108.

* Remove the superfluous call to pthread_exit

Returning from the start function of a thread is specified to
implicitly call pthread_exit().

* Request a reasonably small thread stack

This somewhat mitigates the problem that now the buffer is allocated in
addition to the already allocated thread stack.

Co-authored-by: Johannes Nixdorf <[email protected]>

fiche.c

@@ -587,6 +587,8 @@ static void dispatch_connection(int socket, Fiche_Settings *settings) {
     pthread_attr_destroy(&attr);
 
     // Detach thread if created successfully
+    pthread_attr_destroy(&attr);
+
     // TODO: consider using pthread_tryjoin_np
     pthread_detach(id);