libc: Fix _default_types.h so uint_least8/16/32_t properly recognised by newlib

Newlib built from projectgus/newlib-xtensa 514f105b0
(thanks @Frans-Willem for the fix)

libc/xtensa-lx106-elf/include/machine/_default_types.h

@@ -32,15 +32,19 @@ typedef unsigned long long __uint64_t;
 
 typedef __int8_t __int_least8_t;
 typedef __uint8_t __uint_least8_t;
+#define ___int_least8_t_defined
 
 typedef __int16_t __int_least16_t;
 typedef __uint16_t __uint_least16_t;
+#define ___int_least16_t_defined
 
 typedef __int32_t __int_least32_t;
 typedef __uint32_t __uint_least32_t;
+#define ___int_least32_t_defined
 
 typedef __int64_t __int_least64_t;
 typedef __uint64_t __uint_least64_t;
+#define ___int_least64_t_defined
 
 typedef __INTPTR_TYPE__ __intptr_t;
 typedef __UINTPTR_TYPE__ __uintptr_t;