Fix thinlto tests

Many thintlo tests were broken by a recent change to how musl accesses
the current local (#26486).

See #26506

Author: sbc100

.circleci/config.yml

@@ -705,6 +705,7 @@ jobs:
             lto0.test_exceptions_allowed_uncaught
             lto0.test_longjmp_standalone_standalone
             lto0.test_embind_i64_val
+            thinlto0.test_pthread_dlsym
             core3
             core2g.test_externref
             corez.test_dylink_iostream

tools/system_libs.py

@@ -1080,6 +1080,8 @@ class libc(MuslInternalLibrary,
 
   def __init__(self, **kwargs):
     self.non_lto_files = self.get_libcall_files()
+    # TODO(https://github.com/emscripten-core/emscripten/issues/26506)
+    self.non_lto_files.append(utils.path_from_root('system/lib/libc/musl/src/locale/uselocale.c'))
     super().__init__(**kwargs)
 
   def get_libcall_files(self):