Fix broken link-command-line ordering for libpgfeutils.
In the frontend Makefiles that pull in libpgfeutils, we'd generally done it like this: LDFLAGS += -L$(top_builddir)/src/fe_utils -lpgfeutils $(libpq_pgport) That method is badly broken, as seen in bug #14742 from Chris Ruprecht. The -L flag for src/fe_utils ends up being placed after whatever random -L flags are in LDFLAGS already. That puts us at risk of pulling in libpgfeutils.a from some previous installation rather than the freshly built one in src/fe_utils. Also, the lack of an "override" is hazardous if someone tries to specify some LDFLAGS on the make command line. The correct way to do it is like this: override LDFLAGS := -L$(top_builddir)/src/fe_utils -lpgfeutils $(libpq_pgport) $(LDFLAGS) so that libpgfeutils, along with libpq, libpgport, and libpgcommon, are guaranteed to be pulled in from the build tree and not from any referenced system directory, because their -L flags will appear first. In some places we'd been even lazier and done it like this: LDFLAGS += -L$(top_builddir)/src/fe_utils -lpgfeutils -lpq which is subtly wrong in an additional way: on platforms where we can't restrict the symbols exported by libpq.so, it allows libpgfeutils to latch onto libpgport and libpgcommon symbols from libpq.so, rather than directly from those static libraries as intended. This carries hazards like those explained in the comments for the libpq_pgport macro. In addition to fixing the broken libpgfeutils usages, I tried to standardize on using $(libpq_pgport) like so: override LDFLAGS := $(libpq_pgport) $(LDFLAGS) even where libpgfeutils is not in the picture. This makes no difference right now but will hopefully discourage future mistakes of the same ilk. And it's more like the way we handle CPPFLAGS in libpq-using Makefiles. In passing, just for consistency, make pgbench include PTHREAD_LIBS the same way everyplace else does, ie just after LIBS rather than in some random place in the command line. This might have practical effect if there are -L switches in that macro on some platform. It looks to me like the MSVC build scripts are not affected by this error, but someone more familiar with them than I might want to double check. Back-patch to 9.6 where libpgfeutils was introduced. In 9.6, the hazard this error creates is that a reinstallation might link to the prior installation's copy of libpgfeutils.a and thereby fail to absorb a minor-version bug fix. Discussion: https://postgr.es/m/20170714125106.9231.13772@wrigleys.postgresql.org
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