Fix unportable definition of BSWAP64() macro.

We have a portable way of writing uint64 constants, but whoever wrote
this macro didn't know about it.

While at it, fix unsafe under-parenthesization of arguments.  That might
be moot, because there are already good reasons not to use the macro on
anything more complicated than a simple variable, but it's still poor
practice.

Per buildfarm warnings.

src/include/port/pg_bswap.h

@@ -6,6 +6,7 @@
  * Macros for reversing the byte order of 32-bit and 64-bit unsigned integers.
  * For example, 0xAABBCCDD becomes 0xDDCCBBAA.  These are just wrappers for
  * built-in functions provided by the compiler where support exists.
+ * Elsewhere, beware of multiple evaluations of the arguments!
  *
  * Note that the GCC built-in functions __builtin_bswap32() and
  * __builtin_bswap64() are documented as accepting single arguments of type
@@ -24,23 +25,23 @@
 #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))
+#define BSWAP32(x) ((((x) << 24) & 0xff000000) | \
+					(((x) << 8)  & 0x00ff0000) | \
+					(((x) >> 8)  & 0x0000ff00) | \
+					(((x) >> 24) & 0x000000ff))
 #endif   /* HAVE__BUILTIN_BSWAP32 */
 
 #ifdef HAVE__BUILTIN_BSWAP64
 #define BSWAP64(x) __builtin_bswap64(x)
 #else
-#define BSWAP64(x) (((x << 56) & 0xff00000000000000UL) | \
-					((x << 40) & 0x00ff000000000000UL) | \
-					((x << 24) & 0x0000ff0000000000UL) | \
-					((x << 8) & 0x000000ff00000000UL) | \
-					((x >> 8) & 0x00000000ff000000UL) | \
-					((x >> 24) & 0x0000000000ff0000UL) | \
-					((x >> 40) & 0x000000000000ff00UL) | \
-					((x >> 56) & 0x00000000000000ffUL))
+#define BSWAP64(x) ((((x) << 56) & UINT64CONST(0xff00000000000000)) | \
+					(((x) << 40) & UINT64CONST(0x00ff000000000000)) | \
+					(((x) << 24) & UINT64CONST(0x0000ff0000000000)) | \
+					(((x) << 8)  & UINT64CONST(0x000000ff00000000)) | \
+					(((x) >> 8)  & UINT64CONST(0x00000000ff000000)) | \
+					(((x) >> 24) & UINT64CONST(0x0000000000ff0000)) | \
+					(((x) >> 40) & UINT64CONST(0x000000000000ff00)) | \
+					(((x) >> 56) & UINT64CONST(0x00000000000000ff)))
 #endif   /* HAVE__BUILTIN_BSWAP64 */
 
 /*