pgsql: Use C library functions instead of Abs() for int64

Use C library functions instead of Abs() for int64

Instead of Abs() for int64, use the C standard functions labs() or
llabs() as appropriate.  Define a small wrapper around them that
matches our definition of int64.  (labs() is C90, llabs() is C99.)

Reviewed-by: Zhang Mingli <zmlpostgres@gmail.com>
Reviewed-by: Tom Lane <tgl@sss.pgh.pa.us>
Discussion: https://www.postgresql.org/message-id/flat/4beb42b5-216b-bce8-d452-d924d5794c63%40enterprisedb.com

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/357cfefb09115292cfb98d504199e6df8201c957

Modified Files
--------------
contrib/btree_gist/btree_cash.c  | 2 +-
contrib/btree_gist/btree_int8.c  | 2 +-
src/backend/utils/adt/datetime.c | 8 ++++----
src/backend/utils/adt/dbsize.c   | 2 +-
src/include/c.h                  | 9 +++++++++
5 files changed, 16 insertions(+), 7 deletions(-)