build: Use absolute buildir pathnames in PATH variable

This makes sure that even if any subprocess changes directory, the PATH
environment variable will keep being correct.

check.am

@@ -25,7 +25,7 @@ check-clean:
 
 check-local: $(test_data) $(test_programs) $(test_scripts)
 	[ -z "$(test_tmpdir)" ] || $(MKDIR_P) $(test_tmpdir)
-	PATH="$(top_builddir)/src:$(top_builddir)/scripts:$(top_builddir)/utils:$(PATH)" \
+	PATH="$(abs_top_builddir)/src:$(abs_top_builddir)/scripts:$(abs_top_builddir)/utils:$(PATH)" \
 	  LC_ALL=C \
 	  $(TEST_ENV_VARS) \
 	  srcdir=$(srcdir) builddir=$(builddir) \

debian/changelog

@@ -8,6 +8,7 @@ dpkg (1.18.4) UNRELEASED; urgency=low
     - Set PERL5LIB globally for the test suite to the local modules directory,
       to avoid using the system modules. Regression introduced in dpkg 1.17.8.
       Reported by Jérémy Bobbio <lunar@debian.org>. Closes: #801329
+    - Use absolute buildir pathnames in PATH variable for the test suite.
   * Documentation:
     - Move description for “target architecture” from the dpkg-architecture(1)
       ‘-A’ option to the TERMS section. Closes: #799046