Update pkg-config to 0.29.1.

pkg-config 0.29.1
=================

- Fixed a regression from 0.29 with unquoting values queried with
  --variable. In some cases, this would cause shell special characters to
  be escaped in ways they weren't before. Instead, the unquoting only
  occurs if the value appears to be quoted. (#93284)
- Add support for building pkg-config with Microsoft Visual Studio.
  Thanks to Chun-wei Fan for the fix. (#92489)
- Allow overriding pkg-config variables with environment variables. By
  setting an environment variable of the form
  PKG_CONFIG_$PACKAGE_$VARIABLE, a pkg-config variable can be set
  globally without always having to pass --define-variable. Thanks to
  Alex Larsson for the fix. (#90917)
- Honor -Wl,-framework in addition to -framework so that multiple
  frameworks are handled on OSX. (#1278)
- Fix the OSX build using --with-internal-glib. Thanks to Rud叩 Moura for
  the initial fix and Adam Mercer for testing the final patch. (#92902)

(wiz)