Use a less misleading name for the code that sets up the main thread.

Change-Id: I50c1b0a3b633cf8bc40a6bd86f12adb6b91e2888
diff --git a/libc/private/bionic_tls.h b/libc/private/bionic_tls.h
index 30dc0eb..d92d9d9 100644
--- a/libc/private/bionic_tls.h
+++ b/libc/private/bionic_tls.h
@@ -114,7 +114,7 @@
 
 #if defined(__cplusplus)
 class KernelArgumentBlock;
-extern __LIBC_HIDDEN__ void __libc_init_tls(KernelArgumentBlock& args);
+extern __LIBC_HIDDEN__ void __libc_init_main_thread(KernelArgumentBlock& args);
 #endif
 
 #endif /* __BIONIC_PRIVATE_BIONIC_TLS_H_ */