make __init_tp function static when static linking

this slightly reduces the code size cost of TLS/thread-pointer for
static linking since __init_tp can be inlined into its only caller and
removed. this is analogous to the handling of __init_libc in
__libc_start_main, where the function only has external linkage when
it needs to be called from the dynamic linker.

src/env/__init_tls.c

@@ -8,6 +8,9 @@
 #include "atomic.h"
 #include "syscall.h"
 
+#ifndef SHARED
+static
+#endif
 int __init_tp(void *p)
 {
 	pthread_t td = p;