Replace index_in_[sub]str_array with index_in_[sub]strings,

which scans thru "abc\0def\0123\0\0" type strings. Saves 250 bytes.

   text    data     bss     dec     hex filename
 781266    1328   11844  794438   c1f46 busybox_old
 781010    1328   11844  794182   c1e46 busybox_unstripped

libbb/compare_string_array.c

@@ -19,8 +19,23 @@ int index_in_str_array(const char * const string_array[], const char *key)
 	return -1;
 }
 
+int index_in_strings(const char *strings, const char *key)
+{
+	int idx = 0;
+
+	while (strings[0]) {
+		if (strcmp(strings, key) == 0) {
+			return idx;
+		}
+		strings += strlen(strings) + 1; /* skip NUL */
+		idx++;
+	}
+	return -1;
+}
+
 /* returns the array index of the string, even if it matches only a beginning */
 /* (index of first match is returned, or -1) */
+#ifdef UNUSED
 int index_in_substr_array(const char * const string_array[], const char *key)
 {
 	int i;
@@ -34,3 +49,21 @@ int index_in_substr_array(const char * const string_array[], const char *key)
 	}
 	return -1;
 }
+#endif
+
+int index_in_substrings(const char *strings, const char *key)
+{
+	int len = strlen(key);
+
+	if (len) {
+		int idx = 0;
+		while (strings[0]) {
+			if (strncmp(strings, key, len) == 0) {
+				return idx;
+			}
+			strings += strlen(strings) + 1; /* skip NUL */
+			idx++;
+		}
+	}
+	return -1;
+}