Reorganize our CRC source files again.

Now that we use CRC-32C in WAL and the control file, the "traditional" and
"legacy" CRC-32 variants are not used in any frontend programs anymore.
Move the code for those back from src/common to src/backend/utils/hash.

Also move the slicing-by-8 implementation (back) to src/port. This is in
preparation for next patch that will add another implementation that uses
Intel SSE 4.2 instructions to calculate CRC-32C, where available.

src/include/port/pg_crc32c.h

@@ -0,0 +1,49 @@
+/*-------------------------------------------------------------------------
+ *
+ * pg_crc32c.h
+ *	  Routines for computing CRC-32C checksums.
+ *
+ *
+ * Portions Copyright (c) 1996-2015, PostgreSQL Global Development Group
+ * Portions Copyright (c) 1994, Regents of the University of California
+ *
+ * src/include/port/pg_crc32c.h
+ *
+ *-------------------------------------------------------------------------
+ */
+#ifndef PG_CRC32C_H
+#define PG_CRC32C_H
+
+typedef uint32 pg_crc32c;
+
+#define INIT_CRC32C(crc) ((crc) = 0xFFFFFFFF)
+#define EQ_CRC32C(c1, c2) ((c1) == (c2))
+
+/*
+ * Use slicing-by-8 algorithm.
+ *
+ * On big-endian systems, the intermediate value is kept in reverse byte
+ * order, to avoid byte-swapping during the calculation. FIN_CRC32C reverses
+ * the bytes to the final order.
+ */
+#define COMP_CRC32C(crc, data, len) \
+	((crc) = pg_comp_crc32c_sb8((crc), (data), (len)))
+#ifdef WORDS_BIGENDIAN
+
+#ifdef HAVE__BUILTIN_BSWAP32
+#define BSWAP32(x) __builtin_bswap32(x)
+#else
+#define BSWAP32(x) (((x << 24) & 0xff000000) | \
+					((x << 8) & 0x00ff0000) | \
+					((x >> 8) & 0x0000ff00) | \
+					((x >> 24) & 0x000000ff))
+#endif
+
+#define FIN_CRC32C(crc) ((crc) = BSWAP32(crc) ^ 0xFFFFFFFF)
+#else
+#define FIN_CRC32C(crc) ((crc) ^= 0xFFFFFFFF)
+#endif
+
+extern pg_crc32c pg_comp_crc32c_sb8(pg_crc32c crc, const void *data, size_t len);
+
+#endif /* PG_CRC32C_H */