Revert "[builtins] Try to ensure single copy of emulated TLS state"

This reverts commit b8f04a6 for Apple
Clang. This upstream change now causes dylibs in our SDK to unnecessarily export
this symbol from the builtin static archives.

The long term solution should be to disable emulated TLS support
on Darwin entirely since its already supported natively.

Resolves: <rdar://92713838>
(cherry picked from commit 14942c5)

Author: cyndyishida

compiler-rt/lib/builtins/emutls.c

@@ -374,21 +374,6 @@ emutls_get_address_array(uintptr_t index) {
   return array;
 }
 
-#ifndef _WIN32
-// Our emulated TLS implementation relies on local state (e.g. for the pthread
-// key), and if we duplicate this state across different shared libraries,
-// accesses to the same TLS variable from different shared libraries will yield
-// different results (see https://github.com/android/ndk/issues/1551 for an
-// example). __emutls_get_address is the only external entry point for emulated
-// TLS, and by making it default visibility and weak, we can rely on the dynamic
-// linker to coalesce multiple copies at runtime and ensure a single unique copy
-// of TLS state. This is a best effort; it won't work if the user is linking
-// with -Bsymbolic or -Bsymbolic-functions, and it also won't work on Windows,
-// where the dynamic linker has no notion of coalescing weak symbols at runtime.
-// A more robust solution would be to create a separate shared library for
-// emulated TLS, to ensure a single copy of its state.
-__attribute__((visibility("default"), weak))
-#endif
 void *__emutls_get_address(__emutls_control *control) {
   uintptr_t index = emutls_get_index(control);
   emutls_address_array *array = emutls_get_address_array(index--);