Allow zlib to find external installations. (#44694)

* Allow zlib to find external installations.
* Apply suggestions from code review
* Fixed the determine_version function to loop over all of the potential
libraries that could be installed by zlib.

---------

Co-authored-by: John W. Parent <45471568+johnwparent@users.noreply.github.com>

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

@@ -8,6 +8,7 @@
 # The AutotoolsPackage causes zlib to fail to build with PGI
 import glob
 import os
+import re
 
 import spack.build_systems.generic
 import spack.build_systems.makefile
@@ -24,6 +25,9 @@ class Zlib(MakefilePackage, Package):
     url = "http://zlib.net/fossils/zlib-1.2.11.tar.gz"
     git = "https://github.com/madler/zlib.git"
 
+    tags = ["core-packages"]
+    libraries = ["libz", "zlib", "zlibstatic", "zlibd", "zlibstaticd"]
+
     version("1.3.1", sha256="9a93b2b7dfdac77ceba5a558a580e74667dd6fede4585b91eefb60f03b72df23")
     version("1.3", sha256="ff0ba4c292013dbc27530b3a81e1f9a813cd39de01ca5e0f8bf355702efa593e")
     version("1.2.13", sha256="b3a24de97a8fdbc835b9833169501030b8977031bcb54b3b3ac13740f846ab30")
@@ -63,6 +67,18 @@ class Zlib(MakefilePackage, Package):
 
     license("Zlib")
 
+    @classmethod
+    def determine_version(cls, lib):
+        for library in cls.libraries:
+            for ext in library_extensions:
+                if ext == "dylib":
+                    pattern = re.compile(rf"{library}\.(\d+\.\d+\.\d+)\.{ext}")
+                else:
+                    pattern = re.compile(rf"{library}\.{ext}\.(\d+\.\d+\.\d+)")
+                    match = re.search(pattern, lib)
+                    if match:
+                        return match.group(1)
+
     @property
     def libs(self):
         shared = "+shared" in self.spec