nptl: Clear TLS area for static binaries.

busybox init checks it has pid 1, but getpid() returns another value
when building busybox statically. This is because the corresponding
area is not cleared when allocated (it is allocated with
MAP_UNINITIALIZED, whose behavior depends on the Linux kernel's
CONFIG_MMAP_ALLOW_UNINITIALIZED).

This patch fixes the problem by explicitly clearing the memory area.

	* libpthread/nptl/sysdeps/generic/libc-tls.c (__libc_tls_setup):
	Clear tlsblock.

Signed-off-by: Mickaël Guêné <mickael.guene@st.com>
Signed-off-by: Christophe Lyon <christophe.lyon@st.com>

libpthread/nptl/sysdeps/generic/libc-tls.c

@@ -162,6 +162,7 @@ __libc_setup_tls (size_t tcbsize, size_t tcbalign)
   tcb_offset = roundup (tcbsize, align ?: 1);
   tlsblock = sbrk (tcb_offset + memsz + max_align
 		     + TLS_PRE_TCB_SIZE + GL(dl_tls_static_size));
+  memset(tlsblock, '\0', tcb_offset + memsz + max_align + TLS_PRE_TCB_SIZE + GL(dl_tls_static_size));
   tlsblock += TLS_PRE_TCB_SIZE;
 # else
   /* In case a model with a different layout for the TCB and DTV