pkgconfig: Accept string for 'libraries' and 'libraries_private'

mesonbuild/modules/pkgconfig.py

@@ -68,6 +68,9 @@ class PkgConfigModule:
                       'may not find it from its \'-l{2}\' linker flag in the ' \
                       '{3!r} pkg-config file.'
                 for l in libs:
+                    if isinstance(l, str):
+                        yield l
+                    else:
                         if l.custom_install_dir:
                             yield '-L${prefix}/%s ' % l.custom_install_dir
                         else:
@@ -97,8 +100,8 @@ class PkgConfigModule:
         for l in libs:
             if hasattr(l, 'held_object'):
                 l = l.held_object
-            if not isinstance(l, (build.SharedLibrary, build.StaticLibrary)):
-                raise mesonlib.MesonException('Library argument not a library object.')
+            if not isinstance(l, (build.SharedLibrary, build.StaticLibrary, str)):
+                raise mesonlib.MesonException('Library argument not a library object nor a string.')
             processed_libs.append(l)
         return processed_libs