Added missing strcat function.

c_functions/missing.c

@@ -0,0 +1,21 @@
+#include "c_types.h"
+#include "mem.h"
+#include "ets_sys.h"
+#include "osapi.h"
+#include "gpio.h"
+#include "os_type.h"
+
+char *_strcat(char *dest, const char *src)
+{
+  size_t i, j;
+  for (i = 0; dest[i] != '\0'; i++);
+
+  for (j = 0; src[j] != '\0'; j++)
+  {
+    dest[i + j] = src[j];
+  }
+
+  dest[i + j] = '\0';
+
+  return dest;
+}