Add missing dependency for vcftools (#42047)

* Add missing dependency
* Change dependency to virtual package
   As suggested :)

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Co-authored-by: James Beal <jb23@sanger.ac.uk>

var/spack/repos/builtin/packages/vcftools/package.py

@@ -25,6 +25,7 @@ class Vcftools(AutotoolsPackage):
 
     depends_on("perl", type=("build", "run"))
     depends_on("zlib-api")
+    depends_on("pkgconfig")
 
     # this needs to be in sync with what setup_run_environment adds to
     # PERL5LIB below