use pragma once instead of include guard, it's been

widely supported by almost all compilers.

ref: https://www.wikiwand.com/en/Pragma_once

ext/jaro_winkler/adj_matrix.h

@@ -1,5 +1,4 @@
-#ifndef ADJ_MATRIX_H
-#define ADJ_MATRIX_H
+#pragma once
 #define ADJ_MATRIX_DEFAULT_LENGTH 958
 #define ADJ_MATRIX_SEED 9527
 
@@ -17,6 +16,4 @@ AdjMatrix* adj_matrix_new    (unsigned int length);
 void       adj_matrix_add    (AdjMatrix *matrix, unsigned long long x, unsigned long long y);
 char       adj_matrix_find   (AdjMatrix *matrix, unsigned long long x, unsigned long long y);
 void       adj_matrix_free   (AdjMatrix *matrix);
-AdjMatrix* adj_matrix_default();
-
-#endif
+AdjMatrix* adj_matrix_default();

ext/jaro_winkler/code.h

@@ -1,7 +1,4 @@
-#ifndef CODE_H
-#define CODE_H
+#pragma once
 
 void utf_char_to_code(char *str, unsigned long long *ret_code, int *ret_byte_length);
-void string_to_codes(char *str, int length, unsigned long long **ret_codes, int *ret_length);
-
-#endif
+void string_to_codes(char *str, int length, unsigned long long **ret_codes, int *ret_length);

ext/jaro_winkler/jaro.h

@@ -1,5 +1,4 @@
-#ifndef LIBJARO_JARO_H
-#define LIBJARO_JARO_H
+#pragma once
 
 #define DEFAULT_WEIGHT 0.1
 #define DEFAULT_THRESHOLD 0.7
@@ -12,6 +11,4 @@ typedef struct LibJaroOption{
 
 static const LibJaroOption DEFAULT_OPT = {.weight = DEFAULT_WEIGHT, .threshold = DEFAULT_THRESHOLD, .ignore_case = 0, .adj_table = 0};
 double jaro_distance(char *str1, int len1, char *str2, int len2, LibJaroOption *opt);
-double jaro_winkler_distance(char *str1, int len1, char *str2, int len2, LibJaroOption *opt);
-
-#endif
+double jaro_winkler_distance(char *str1, int len1, char *str2, int len2, LibJaroOption *opt);