App.get_libname(): Don't use get_proj_refs()

App.get_projects_refs() is a versatile tool, but what it does isn't obvious. Use the simpler method .get_value() instead for get_libname(), and return None if a project doesn't provide a linkable library.
This is similar to fix aadcdfb5f.
Signed-off-by: Jan Lindemann <jan@janware.com>

src/python/jw/pkg/App.py

@@ -639,20 +639,14 @@ class App(Base):
                             ret.append(m)
         return ret
 
-    def get_libname(self, projects) -> str:
-        vals = self.get_project_refs(
-            projects,
-            ['build'],
-            'libname',
-            scope = Scope.One,
-            add_self = False,
-            names_only = True,
-        )
-        if not vals:
-            return ' '.join(projects)
-        if 'none' in vals:
-            vals.remove('none')
-        return ' '.join(reversed(vals))
+    def get_libname(self, spec: str) -> str | None:
+        project_name = self.strip_module_from_spec(spec)
+        ret = self.get_value(project_name, 'build', 'libname')
+        if ret == 'none':
+            return None
+        if ret is None:
+            return project_name
+        return ret
 
     def is_excluded_from_build(self, project: str) -> str | None:
         log(DEBUG, 'checking if project ' + project + ' is excluded from build')

src/python/jw/pkg/cmds/projects/CmdLdflags.py

@@ -45,8 +45,8 @@ class CmdLdflags(Cmd):  # export
         for m in deps:
             if m in exclude:
                 continue
-            libname = self.app.get_libname([m])
-            if not len(libname):
+            libname = self.app.get_libname(m)
+            if libname is None:
                 continue
             path = self.app.find_dir(m, ['/lib'])
             if not path:
@@ -69,8 +69,9 @@ class CmdLdflags(Cmd):  # export
         for m in reversed(deps):
             if m in args.exclude:
                 continue
-            libname = self.app.get_libname([m])
-            if len(libname):
+            libname = self.app.get_libname(m)
+            if libname is None:
+                continue
             out.append('-l' + libname)
         if not out:
             return