musl has a conservative stacksize, as compared to glibc, so treat it
like other systems with such stacksize

diff --git a/thread_pthread.c b/thread_pthread.c
index 951885ffa0..e2d662143b 100644
--- a/thread_pthread.c
+++ b/thread_pthread.c
@@ -721,7 +721,7 @@ ruby_init_stack(volatile VALUE *addr
 {
     native_main_thread.id = pthread_self();
 
-#if MAINSTACKADDR_AVAILABLE
+#if MAINSTACKADDR_AVAILABLE && !(defined(__linux__) && !defined(__GLIBC__))
     if (native_main_thread.stack_maxsize) return;
     {
        void* stackaddr;
@@ -1680,7 +1680,7 @@ ruby_stack_overflowed_p(const rb_thread_t *th, const void *addr)

 #ifdef STACKADDR_AVAILABLE
     if (get_stack(&base, &size) == 0) {
-# ifdef __APPLE__
+# if defined(__APPLE__) || (defined(__linux__) && !defined(__GLIBC__))
 	if (pthread_equal(th->thread_id, native_main_thread.id)) {
 	    struct rlimit rlim;
 	    if (getrlimit(RLIMIT_STACK, &rlim) == 0 && rlim.rlim_cur > size) {