pgsql: Add functions gcd() and lcm() for integer and numeric types.

Add functions gcd() and lcm() for integer and numeric types.

These compute the greatest common divisor and least common multiple of
a pair of numbers using the Euclidean algorithm.

Vik Fearing, reviewed by Fabien Coelho.

Discussion: https://postgr.es/m/adbd3e0b-e3f1-5bbc-21db-03caf1cef0f7@2ndquadrant.com

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/13661ddd7eaec7e2809ff5c29fc14653b6161036

Modified Files
--------------
doc/src/sgml/func.sgml                |  34 +++++++
src/backend/utils/adt/int.c           | 126 +++++++++++++++++++++++++
src/backend/utils/adt/int8.c          | 126 +++++++++++++++++++++++++
src/backend/utils/adt/numeric.c       | 171 ++++++++++++++++++++++++++++++++++
src/include/catalog/catversion.h      |   2 +-
src/include/catalog/pg_proc.dat       |  20 ++++
src/test/regress/expected/int4.out    |  46 +++++++++
src/test/regress/expected/int8.out    |  46 +++++++++
src/test/regress/expected/numeric.out |  44 +++++++++
src/test/regress/sql/int4.sql         |  25 +++++
src/test/regress/sql/int8.sql         |  25 +++++
src/test/regress/sql/numeric.sql      |  25 +++++
12 files changed, 689 insertions(+), 1 deletion(-)