Defend against -fstack-protector in libc startup.

Exactly which functions get a stack protector is up to the compiler, so
let's separate the code that sets up the environment stack protection
requires and explicitly build it with -fno-stack-protector.

Bug: http://b/26276517
Change-Id: I8719e23ead1f1e81715c32c1335da868f68369b5
diff --git a/libc/private/bionic_tls.h b/libc/private/bionic_tls.h
index 2ca7728..9d3f4c5 100644
--- a/libc/private/bionic_tls.h
+++ b/libc/private/bionic_tls.h
@@ -121,7 +121,7 @@
 
 #if defined(__cplusplus)
 class KernelArgumentBlock;
-extern __LIBC_HIDDEN__ void __libc_init_main_thread(KernelArgumentBlock& args);
+extern __LIBC_HIDDEN__ void __libc_init_main_thread(KernelArgumentBlock&);
 #endif
 
 #endif /* __BIONIC_PRIVATE_BIONIC_TLS_H_ */