rustc: Don't export builtins/panic/alloc syms

This hides symbols from various unstable and implementation-detail
crates of the standard library. Although typically transitive exported
`pub extern` functions are exported from cdylibs, these crates aren't
necessary as they're all implementation details.

Closes #34493

1 files changed, 6 insertions, 0 deletions

diff --git a/src/liballoc_jemalloc/pthread_atfork_dummy.c b/src/liballoc_jemalloc/pthread_atfork_dummy.c
new file mode 100644
index 00000000000..f798afe741f
--- /dev/null
+++ b/src/liballoc_jemalloc/pthread_atfork_dummy.c
@@ -0,0 +1,6 @@
+// See comments in build.rs for why this exists
+int pthread_atfork(void* prefork,
+                   void* postfork_parent,
+                   void* postfork_child) {
+  return 0;
+}