tar: conditionally link iconv (spack#47933)

* fix broken packages requiring iconv

* tar: -liconv only when libiconv

* Revert "fix broken packages requiring iconv"

This reverts commit 5fa426b.

---------

Co-authored-by: Harmen Stoppels <[email protected]>

Author: kftsehk

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

@@ -72,7 +72,7 @@ def determine_version(cls, exe):
         return match.group(1) if match else None
 
     def flag_handler(self, name, flags):
-        if name == "ldflags" and self.spec.satisfies("@1.35"):
+        if name == "ldflags" and self.spec.satisfies("@1.35 ^[virtuals=iconv] libiconv"):
             # https://savannah.gnu.org/bugs/?64441
             flags.append("-liconv")
         return (flags, None, None)