pgsql: Inline the easy cases in MakeExpandedObjectReadOnly().

Inline the easy cases in MakeExpandedObjectReadOnly().

This attempts to buy back some of whatever performance we lost from fixing
bug #14174 by inlining the initial checks in MakeExpandedObjectReadOnly()
into the callers. We can do that in a macro without creating multiple-
evaluation hazards, so it's pretty much free notationally; and the amount
of code added to callers should be minimal as well. (Testing a value can't
take many more instructions than passing it to a subroutine.)

Might as well inline DatumIsReadWriteExpandedObject() while we're at it.

This is an ABI break for callers, so it doesn't seem safe to put into 9.5,
but I see no reason not to do it in HEAD.

Branch
------
master

Details
-------
http://git.postgresql.org/pg/commitdiff/d50183c5786a21910bac566d2987f955c7bc1d62

Modified Files
--------------
src/backend/utils/adt/expandeddatum.c | 26 ++++----------------------
src/include/utils/expandeddatum.h | 12 ++++++++++--
2 files changed, 14 insertions(+), 24 deletions(-)