pgsql: Further fix install program detection

Further fix install program detection

The $(or) make function was introduced in GNU make 3.81, so the
previous coding didn't work in 3.80. Write it differently, and
improve the variable naming to make more sense in the new coding.

Branch
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master

Details
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http://git.postgresql.org/pg/commitdiff/dcd5af6c3498a265053aa3292d41c3946e225627

Modified Files
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configure | 6 +++---
configure.in | 6 +++---
src/Makefile.global.in | 3 ++-
3 files changed, 8 insertions(+), 7 deletions(-)