pgsql: Record full paths of programs sought by "configure".

Record full paths of programs sought by "configure".

Previously we had a mix of uses of AC_CHECK_PROG[S] and AC_PATH_PROG[S].
The only difference between those macros is that the latter emits the
full path to the program it finds, eg "/usr/bin/prove", whereas the
former emits just "prove". Let's standardize on always emitting the
full path; this is better for documentation of the build, and it might
prevent some types of failures if later build steps are done with
a different PATH setting.

I did not touch the AC_CHECK_PROG[S] calls in ax_pthread.m4 and
ax_prog_perl_modules.m4. There seems no need to make those diverge from
upstream, since we do not record the programs sought by the former, while
the latter's call to AC_CHECK_PROG(PERL,...) will never be reached.

Discussion: https://postgr.es/m/25937.1501433410@sss.pgh.pa.us

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/40b9f192170a300cd9456eb71ba7c792ba9533e1

Modified Files
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config/docbook.m4 | 2 +-
config/programs.m4 | 6 +-
configure | 285 +++++++++++++++++++++++++++++++----------------------
configure.in | 22 ++---
4 files changed, 180 insertions(+), 135 deletions(-)