string/strdupa: support strdupa strndupa

refs:https://sites.uclouvain.be/SystInfo/manpages/man3/strdup.3.html

Signed-off-by: dongjiuzhu1 <dongjiuzhu1@xiaomi.com>

include/string.h

@@ -29,15 +29,25 @@
 #include <nuttx/compiler.h>
 
 #include <stddef.h>
+#include <alloca.h>
 
 /****************************************************************************
  * Pre-processor Definitions
  ****************************************************************************/
 
 #define strcoll_l(s1, s2, l)    strcoll(s1, s2)
+#define strdupa(x)              strcpy(alloca(strlen(x) + 1), x)
 #define strerror_l(e, l)        strerror(e)
 #define strxfrm_l(s1, s2, n, l) strxfrm(s1, s2, n)
 
+#define strndupa(x, l) ({ \
+  FAR const char *__old = (x); \
+  size_t __len = strnlen(__old, (l)); \
+  FAR char *__new = alloca(__len + 1); \
+  __new[__len] = '\0'; \
+  (FAR char *)memcpy(__new, __old, __len); \
+})
+
 /****************************************************************************
  * Public Function Prototypes
  ****************************************************************************/