find_libraries searches lib and lib64 before prefix (#11958)

The default library search for a package checks the lib/ and lib64/
directories for libraries before the root prefix, in order to save
time when searching for libraries provided by externals (which e.g.
may have '/usr/' as their root).

This moves that logic into the "find_libraries" utility method so
packages implementing their own custom library search logic can
benefit from it.

This also updates packages which appear to be replicating this logic
exactly, replacing it with a single call to "find_libraries".

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

@@ -63,14 +63,8 @@ def install(self, spec, prefix):
 
     @property
     def libs(self):
-        prefix = self.prefix
-        search_paths = [(prefix.lib, False), (prefix.lib64, False),
-                        (prefix, True)]
-        for search_root, recursive in search_paths:
-            libs = find_libraries(
-                'libcuda', root=search_root, shared=True, recursive=recursive)
-            if libs:
-                break
+        libs = find_libraries('libcuda', root=self.prefix, shared=True,
+                              recursive=True)
 
         filtered_libs = []
         # CUDA 10.0 provides Compatability libraries for running newer versions

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

@@ -150,12 +150,7 @@ def libs(self):
         """Export the hypre library.
         Sample usage: spec['hypre'].libs.ld_flags
         """
-        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
+        libs = find_libraries('libHYPRE', root=self.prefix, shared=is_shared,
+                              recursive=True)
+        return libs or None

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

@@ -500,12 +500,9 @@ def libs(self):
             # Q: should the result be ordered by dependency?
         else:
             sun_libs = ['libsundials_' + p for p in query_parameters]
-        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(sun_libs, root=path, shared=is_shared,
-                                  recursive=recursive)
-            if libs:
-                return libs
-        return None  # Raise an error
+
+        libs = find_libraries(sun_libs, root=self.prefix, shared=is_shared,
+                              recursive=True)
+
+        return libs or None  # Raise an error if no libs are found