pgsql: When in automatic dependency mode, never delete any intermediate

Log Message:
-----------
When in automatic dependency mode, never delete any intermediate
files automatically. Otherwise, the following could happen: When
starting from a clean source tree, the first build would delete the
intermediate file, but also create the dependency file, which
mentions the intermediate file, thus making it non-intermediate.
The second build will then need to rebuild the now non-intermediate
missing file. So the second build will do work even though nothing
had changed. One place where this happens is the .c -> .o -> .so
chain for some contrib modules.

Modified Files:
--------------
pgsql/src:
Makefile.global.in (r1.264 -> r1.265)
(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/Makefile.global.in?r1=1.264&r2=1.265)