Define _STRING_ARCH_unaligned unconditionally

[Adhemerval Zanella]

This is a respin on my initial try to remove the undefined _STRING_ARCH_unaligned
from PPC64 builds, but now extended to all arch that do not define it.  This patch
defines _STRING_ARCH_unaligned to 0, mimicking old undefined behavior.

--

	* bits/string.h (_STRING_ARCH_unaligned): Define it to 0.

---

diff --git a/bits/string.h b/bits/string.h
index f8630d2..42516d4 100644
--- a/bits/string.h
+++ b/bits/string.h
@@ -8,5 +8,6 @@
 #ifndef _BITS_STRING_H
 #define _BITS_STRING_H	1
 
+#define _STRING_ARCH_unaligned   0
 
 #endif /* bits/string.h */