[libc] Allow CPU architectures to use unoptimised string functions

Signed-off-by: Michael Brown <mcb30@ipxe.org>

src/include/string.h

 FILE_LICENCE ( GPL2_OR_LATER_OR_UBDL );
 
 #include <stddef.h>
+
+extern void * generic_memset ( void *dest, int character,
+			       size_t len ) __nonnull;
+extern void * generic_memcpy ( void *dest, const void *src,
+			       size_t len ) __nonnull;
+extern void * generic_memmove ( void *dest, const void *src,
+				size_t len ) __nonnull;
+
 #include <bits/string.h>
 
 /* Architecture-specific code is expected to provide these functions,
 void * memset ( void *dest, int character, size_t len ) __nonnull;
 void * memcpy ( void *dest, const void *src, size_t len ) __nonnull;
 void * memmove ( void *dest, const void *src, size_t len ) __nonnull;
-extern void * generic_memset ( void *dest, int character,
-			       size_t len ) __nonnull;
-extern void * generic_memcpy ( void *dest, const void *src,
-			       size_t len ) __nonnull;
-extern void * generic_memmove ( void *dest, const void *src,
-				size_t len ) __nonnull;
 
 extern int __pure memcmp ( const void *first, const void *second,
 			   size_t len ) __nonnull;