dylink: Add test for relocations within the TLS data (#18641)

Depends on https://reviews.llvm.org/D143020

Author: sbc100

src/library_pthread.js

@@ -231,7 +231,7 @@ var LibraryPThread = {
     // Called by worker.js each time a thread is started.
     threadInitTLS: function() {
 #if PTHREADS_DEBUG
-      dbg('threadInitTLS.');
+      dbg('threadInitTLS');
 #endif
       // Call thread init functions (these are the _emscripten_tls_init for each
       // module loaded.

test/pthread/test_pthread_tls_dylink.c

@@ -0,0 +1,36 @@
+#include <assert.h>
+#include <pthread.h>
+#include <stdio.h>
+
+int foo = 3;
+// This should generate a relocation in data section
+static int* _Atomic foo_addr = &foo;
+// This should generate a reloction in the TLS data section
+static _Thread_local int *tls_foo_addr = &foo;
+
+void run_test() {
+  printf("&foo         : %p\n", &foo);
+  printf("&foo_addr    : %p\n", &foo_addr);
+  printf("&tls_foo_addr: %p\n", &tls_foo_addr);
+  // The values stored foo_addr and tls_foo_addr should both be
+  // the address of foo
+  printf("foo_add=%p tls_foo_addr=%p [delta=%ld]\n", foo_addr, tls_foo_addr, foo_addr - tls_foo_addr);
+  assert(foo_addr == &foo);
+  assert(tls_foo_addr == &foo);
+}
+
+void* thread_main(void* arg) {
+  run_test();
+  return NULL;
+}
+
+int main() {
+  run_test();
+
+  pthread_t t;
+  pthread_create(&t, NULL, thread_main, NULL);
+  pthread_join(t, NULL);
+
+  printf("done\n");
+  return 0;
+}

test/pthread/test_pthread_tls_dylink.out

@@ -0,0 +1 @@
+done

test/test_core.py

@@ -2849,6 +2849,13 @@ def test_pthread_proxy_to_pthread(self):
     self.set_setting('EXIT_RUNTIME')
     self.do_run_in_out_file_test(test_file('pthread/test_pthread_proxy_to_pthread.c'))
 
+  @node_pthreads
+  @needs_dylink
+  def test_pthread_tls_dylink(self):
+    self.set_setting('MAIN_MODULE', 2)
+    self.emcc_args.append('-Wno-experimental')
+    self.do_run_in_out_file_test('pthread/test_pthread_tls_dylink.c')
+
   def test_tcgetattr(self):
     self.do_runf(test_file('termios/test_tcgetattr.c'), 'success')