pgsql: Optimize popcount functions with ARM SVE intrinsics.

Optimize popcount functions with ARM SVE intrinsics.

This commit introduces SVE implementations of pg_popcount{32,64}.
Unlike the Neon versions, we need an additional configure-time
check to determine if the compiler supports SVE intrinsics, and we
need a runtime check to determine if the current CPU supports SVE
instructions. Our testing showed that the SVE implementations are
much faster for larger inputs and are comparable to the status
quo for smaller inputs.

Author: "Devanga(dot)Susmitha(at)fujitsu(dot)com" <Devanga(dot)Susmitha(at)fujitsu(dot)com>
Co-authored-by: "Chiranmoy(dot)Bhattacharya(at)fujitsu(dot)com" <Chiranmoy(dot)Bhattacharya(at)fujitsu(dot)com>
Co-authored-by: "Malladi, Rama" <ramamalladi(at)hotmail(dot)com>
Reviewed-by: John Naylor <johncnaylorls(at)gmail(dot)com>
Reviewed-by: Kirill Reshke <reshkekirill(at)gmail(dot)com>
Discussion: https://postgr.es/m/010101936e4aaa70-b474ab9e-b9ce-474d-a3ba-a3dc223d295c-000000%40us-west-2.amazonses.com
Discussion: https://postgr.es/m/OSZPR01MB84990A9A02A3515C6E85A65B8B2A2%40OSZPR01MB8499.jpnprd01.prod.outlook.com

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/519338ace410d9b1ffb13176b8802b0307ff0531

Modified Files
--------------
config/c-compiler.m4 | 52 ++++++++
configure | 71 +++++++++++
configure.ac | 9 ++
meson.build | 48 +++++++
src/include/pg_config.h.in | 3 +
src/include/port/pg_bitutils.h | 17 +++
src/port/pg_popcount_aarch64.c | 281 ++++++++++++++++++++++++++++++++++++++++-
7 files changed, 475 insertions(+), 6 deletions(-)