pgsql: Skip unnecessary stat() calls in walkdir().

Skip unnecessary stat() calls in walkdir().

Some kernels can tell us the type of a "dirent", so we can avoid a call
to stat() or lstat() in many cases.  Define a new function
get_dirent_type() to contain that logic, for use by the backend and
frontend versions of walkdir(), and perhaps other callers in future.

Reviewed-by: Tom Lane <tgl@sss.pgh.pa.us>
Reviewed-by: Juan José Santamaría Flecha <juanjo.santamaria@gmail.com>
Discussion: https://postgr.es/m/CA%2BhUKG%2BFzxupGGN4GpUdbzZN%2Btn6FQPHo8w0Q%2BAPH5Wz8RG%2Bww%40mail.gmail.com

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/861c6e7c8e4dfdd842442dde47cc653764baff4f

Modified Files
--------------
src/backend/storage/file/fd.c    |  33 ++++++------
src/common/Makefile              |   2 +-
src/common/file_utils.c          | 109 ++++++++++++++++++++++++++++++++-------
src/include/common/file_utils.h  |  20 ++++++-
src/tools/msvc/Mkvcbuild.pm      |   4 +-
src/tools/pgindent/typedefs.list |   1 +
6 files changed, 129 insertions(+), 40 deletions(-)