pgsql: Use explicit_bzero

Use explicit_bzero

Use the explicit_bzero() function in places where it is important that
security information such as passwords is cleared from memory.  There
might be other places where it could be useful; this is just an
initial collection.

For platforms that don't have explicit_bzero(), provide various
fallback implementations.  (explicit_bzero() itself isn't standard,
but as Linux/glibc, FreeBSD, and OpenBSD have it, it's the most common
spelling, so it makes sense to make that the invocation point.)

Discussion: https://www.postgresql.org/message-id/flat/42d26bde-5d5b-c90d-87ae-6cab875f73be%402ndquadrant.com

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/74a308cf5221f491776fcdb4dc36eb61678dbc6f

Modified Files
--------------
configure                            | 15 +++++++++-
configure.in                         |  2 ++
src/backend/libpq/be-secure-common.c |  3 ++
src/include/pg_config.h.in           |  6 ++++
src/include/pg_config.h.win32        |  6 ++++
src/include/port.h                   |  4 +++
src/interfaces/libpq/fe-connect.c    |  8 ++++++
src/port/explicit_bzero.c            | 55 ++++++++++++++++++++++++++++++++++++
src/tools/msvc/Mkvcbuild.pm          |  2 +-
9 files changed, 99 insertions(+), 2 deletions(-)