pgsql: Fix a few single-file (MODULES, not MODULE_big) contrib makefiles

Log Message:
-----------
Fix a few single-file (MODULES, not MODULE_big) contrib makefiles that were
supposing that they should set SHLIB_LINK rather than LDFLAGS_SL. Since these
don't go through Makefile.shlib that was a no-op on most platforms. Also
regularize the few platform-specific Makefiles that did pay attention to
SHLIB_LINK: it seems that the real value of that is to pull in BE_DLLLIBS,
so do that instead. Per buildfarm failures on cygwin.

Modified Files:
--------------
pgsql/contrib/earthdistance:
Makefile (r1.19 -> r1.20)
(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/contrib/earthdistance/Makefile?r1=1.19&r2=1.20)
pgsql/contrib/spi:
Makefile (r1.28 -> r1.29)
(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/contrib/spi/Makefile?r1=1.28&r2=1.29)
pgsql/contrib/tablefunc:
Makefile (r1.9 -> r1.10)
(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/contrib/tablefunc/Makefile?r1=1.9&r2=1.10)
pgsql/src/makefiles:
Makefile.aix (r1.30 -> r1.31)
(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/makefiles/Makefile.aix?r1=1.30&r2=1.31)
Makefile.cygwin (r1.14 -> r1.15)
(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/makefiles/Makefile.cygwin?r1=1.14&r2=1.15)
Makefile.darwin (r1.12 -> r1.13)
(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/makefiles/Makefile.darwin?r1=1.12&r2=1.13)
Makefile.win32 (r1.16 -> r1.17)
(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/makefiles/Makefile.win32?r1=1.16&r2=1.17)