pgsql: Simplify passing of configure arguments to pg_config

Simplify passing of configure arguments to pg_config

The previous system had configure put the value into the makefiles and
then have the makefiles pass them to the build of pg_config.  That was
put in place when pg_config was a shell script.  We can simplify that
by having configure put the value into pg_config.h directly.  This
also makes the standard build system match how the MSVC build system
already does it.

Discussion: https://www.postgresql.org/message-id/flat/6e457870-cef5-5f1d-b57c-fc89cfb8a788%402ndquadrant.com

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/b691c189c671ca9b88743ed6546b60641e5199e4

Modified Files
--------------
configure                  | 6 ++++--
configure.in               | 2 +-
src/Makefile.global.in     | 3 ---
src/common/Makefile        | 1 -
src/common/config_info.c   | 6 +-----
src/include/pg_config.h.in | 3 +++
src/tools/msvc/Solution.pm | 7 +------
7 files changed, 10 insertions(+), 18 deletions(-)