Convert uses of hash_string_pointer to fasthash equivalent

Remove duplicate hash_string_pointer() function definitions by creating
a new inline function hash_string() for this purpose.

This has the added advantage of avoiding strlen() calls when doing hash
lookup. It's not clear how many of these are perfomance-sensitive
enough to benefit from that, but the simplification is worth it on
its own.

Reviewed by Jeff Davis

Discussion: https://postgr.es/m/CANWCAZbg_XeSeY0a_PqWmWqeRATvzTzUNYRLeT%2Bbzs%2BYQdC92g%40mail.gmail.com

src/bin/pg_rewind/filemap.c

@@ -28,7 +28,7 @@
 
 #include "catalog/pg_tablespace_d.h"
 #include "common/file_utils.h"
-#include "common/hashfn.h"
+#include "common/hashfn_unstable.h"
 #include "common/string.h"
 #include "datapagemap.h"
 #include "filemap.h"
@@ -38,12 +38,11 @@
  * Define a hash table which we can use to store information about the files
  * appearing in source and target systems.
  */
-static uint32 hash_string_pointer(const char *s);
 #define SH_PREFIX		filehash
 #define SH_ELEMENT_TYPE	file_entry_t
 #define SH_KEY_TYPE		const char *
 #define	SH_KEY			path
-#define SH_HASH_KEY(tb, key)	hash_string_pointer(key)
+#define SH_HASH_KEY(tb, key)	hash_string(key)
 #define SH_EQUAL(tb, a, b)		(strcmp(a, b) == 0)
 #define	SH_SCOPE		static inline
 #define SH_RAW_ALLOCATOR	pg_malloc0
@@ -821,15 +820,3 @@ decide_file_actions(void)
 
 	return filemap;
 }
-
-
-/*
- * Helper function for filemap hash table.
- */
-static uint32
-hash_string_pointer(const char *s)
-{
-	unsigned char *ss = (unsigned char *) s;
-
-	return hash_bytes(ss, strlen(s));
-}