sandbox: Rename strdup() functions

These functions include calls to a memory-allocation routine and so need
to use the system routine when called from a library.

To preserve access to these functions for libraries that need it, such as
SDL, rename these functions within U-Boot.
Signed-off-by: NSimon Glass <sjg@chromium.org>

include/linux/string.h

@@ -91,6 +91,11 @@ extern __kernel_size_t strnlen(const char *,__kernel_size_t);
 size_t strcspn(const char *s, const char *reject);
 #endif
 
+#ifdef CONFIG_SANDBOX
+# define strdup		sandbox_strdup
+# define strndup		sandbox_strndup
+#endif
+
 #ifndef __HAVE_ARCH_STRDUP
 extern char * strdup(const char *);
 extern char * strndup(const char *, size_t);