pgsql: pg_test_timing: Also test RDTSC[P] timing, report time source, T

pg_test_timing: Also test RDTSC[P] timing, report time source, TSC frequency

This adds support to pg_test_timing for the different timing sources added by
294520c4448.

Author: Lukas Fittl <lukas@fittl.com>
Author: David Geier <geidav.pg@gmail.com>
Reviewed-by: Andres Freund <andres@anarazel.de>
Reviewed-by: David Geier <geidav.pg@gmail.com>
Reviewed-by: Zsolt Parragi <zsolt.parragi@percona.com>
Reviewed-by: Álvaro Herrera <alvherre@kurilemu.de> (in an earlier version)
Discussion: https://www.postgresql.org/message-id/flat/20200612232810.f46nbqkdhbutzqdg%40alap3.anarazel.de

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/16fca482548382c8d6255319b1c6e5de4afff7f1

Modified Files
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doc/src/sgml/config.sgml                |   6 ++
doc/src/sgml/ref/pgtesttiming.sgml      | 153 ++++++++++++++++++++++++++------
src/bin/pg_test_timing/pg_test_timing.c | 105 ++++++++++++++++++++--
src/include/portability/instr_time.h    |   7 ++
4 files changed, 233 insertions(+), 38 deletions(-)