[hypre] add the 'headers' property (#7278)

* [hypre] Add the 'headers' property plus a small tweak in the 'libs'
property.

* [hypre] Add fallbacks for searching for '.libs' in 'prefix.lib64' and
in all of 'prefix'.

* [hypre] Fix style.

* [hypre] Use find_headers instead of find + HeaderList.

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

@@ -110,8 +110,26 @@ def install(self, spec, prefix):
                         '-rhsone')
             make("install")
 
+    @property
+    def headers(self):
+        """Export the main hypre header, HYPRE.h; all other headers can be found
+        in the same directory.
+        Sample usage: spec['hypre'].headers.cpp_flags
+        """
+        hdrs = find_headers('HYPRE', self.prefix.include, recursive=False)
+        return hdrs or None
+
     @property
     def libs(self):
-        is_shared = self.spec.satisfies('+shared')
+        """Export the hypre library.
-        return find_libraries('libHYPRE', root=self.prefix,
+        Sample usage: spec['hypre'].libs.ld_flags
-                              shared=is_shared, recursive=True)
+        """
+        search_paths = [[self.prefix.lib, False], [self.prefix.lib64, False],
+                        [self.prefix, True]]
+        is_shared = '+shared' in self.spec
+        for path, recursive in search_paths:
+            libs = find_libraries('libHYPRE', root=path,
+                                  shared=is_shared, recursive=recursive)
+            if libs:
+                return libs
+        return None