CMakePackage: allow custom CMAKE_PREFIX_PATH entries (#32547)

* define `cmake_prefix_paths` property for packages

add to CMake arguments via CMakePackage

Co-authored-by: Robert Underwood <runderwood@anl.gov>

var/spack/repos/builtin.mock/packages/define-cmake-prefix-paths/package.py

@@ -0,0 +1,20 @@
+# Copyright 2013-2022 Lawrence Livermore National Security, LLC and other
+# Spack Project Developers. See the top-level COPYRIGHT file for details.
+#
+# SPDX-License-Identifier: (Apache-2.0 OR MIT)
+
+from spack.package import *
+
+
+class DefineCmakePrefixPaths(Package):
+    """Package that defines cmake_prefix_paths"""
+
+    homepage = "http://www.example.com"
+    url = "http://www.example.com/definecmakeprefixpaths-1.0.tar.gz"
+
+    version("1.0", "0123456789abcdef0123456789abcdef")
+
+    @property
+    def cmake_prefix_paths(self):
+        paths = [self.prefix.test]
+        return paths

var/spack/repos/builtin.mock/packages/depends-on-define-cmake-prefix-paths/package.py

@@ -0,0 +1,17 @@
+# Copyright 2013-2022 Lawrence Livermore National Security, LLC and other
+# Spack Project Developers. See the top-level COPYRIGHT file for details.
+#
+# SPDX-License-Identifier: (Apache-2.0 OR MIT)
+
+from spack.package import *
+
+
+class DependsOnDefineCmakePrefixPaths(Package):
+    """Package that defines cmake_prefix_paths"""
+
+    homepage = "http://www.example.com"
+    url = "http://www.example.com/dependsonefinecmakeprefixpaths-1.0.tar.gz"
+
+    version("1.0", "0123456789abcdef0123456789abcdef")
+
+    depends_on("define-cmake-prefix-paths")