builtin: more libc fn definitions

Author: medvednikov

vlib/builtin/cfns.c.v

@@ -177,6 +177,15 @@ fn C.strchr(s &char, c int) &char
 [trusted]
 fn C.getchar() int
 
+[trusted]
+fn C.strdup(s &char) &char
+
+[trusted]
+fn C.strncasecmp(s &char, s2 &char, n int) int
+
+[trusted]
+fn C.strcasecmp(s &char, s2 &char) int
+
 [trusted]
 fn C.strerror(int) &char