output/security_label.source referring to abs_builddir instead of libdir

In make check, there are 4 shared libraries that are loaded for test cases from the src/test/regress folder. Whereas, output of other libraries contain @libdir@ tag, the output file for security_label (dumm_seclabel) contains a tag for @abs_builddir@ in the output/security_label.source file.

I believe this an issue, and rather than referring @abs_builddir@, it should instead contain the tag @libdir@. Also note that while I could provide a path for dynamic libraries via "dlpath" option of pg_regress, this is not honored by security_label test case.

PFA patch for this fix.

Regards.