[COMMITTERS] pgsql: Honor PROVE_FLAGS environment setting

Honor PROVE_FLAGS environment setting

On MSVC builds and on back branches that means removing the hardcoded
--verbose setting. On master for Unix that means removing the empty
setting in the global Makefile so that the value can be acquired from
the environment as well as from the make arguments.

Backpatch to 9.4 where we introduced TAP tests

Branch
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REL9_6_STABLE

Details
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https://git.postgresql.org/pg/commitdiff/cb701af784556e7417bb0d9daa822e913f43b1fa

Modified Files
--------------
src/Makefile.global.in      | 3 ++-
src/test/perl/README        | 5 +++++
src/tools/msvc/vcregress.pl | 5 ++++-
3 files changed, 11 insertions(+), 2 deletions(-)