bstr: preparation for next commit

Just so I can move this file without modifying its contents in the next
commit.

compat/compiler.h is to be moved to osdep/ with the next commit, so add
a dummy header.

bstr/bstr.c

@@ -29,7 +29,7 @@
 
 #include "common/common.h"
 #include "misc/ctype.h"
-#include "bstr/bstr.h"
+#include "bstr.h"
 
 int bstrcmp(struct bstr str1, struct bstr str2)
 {

bstr/bstr.h

@@ -26,7 +26,7 @@
 #include <stdarg.h>
 
 #include "talloc.h"
-#include "compat/compiler.h"
+#include "osdep/compiler.h"
 
 /* NOTE: 'len' is size_t, but most string-handling functions below assume
  * that input size has been sanity checked and len fits in an int.

osdep/compiler.h

@@ -0,0 +1 @@
+#include "compat/compiler.h"