[liba] Add strncmp

liba/include/string.h

@@ -13,6 +13,7 @@ void * memset(void * b, int c, size_t len);
 
 char * strchr(const char * s, int c);
 int strcmp(const char * s1, const char * s2);
+int strncmp(const char * s1, const char * s2, size_t n);
 size_t strlcpy(char * dst, const char * src, size_t len);
 size_t strlen(const char * s);
 

liba/src/strcmp.c

@@ -7,3 +7,14 @@ int strcmp(const char *s1, const char *s2) {
   }
   return (*(unsigned char *)s1) - (*(unsigned char *)s2);
 }
+
+int strncmp(const char *s1, const char *s2, size_t n) {
+  while (n-- > 0) {
+    if (*s1 == NULL || *s2 != *s1) {
+      return (*(unsigned char *)s1) - (*(unsigned char *)s2);
+    }
+    s1++;
+    s2++;
+  }
+  return 0;
+}