giflib: add config.yml + msys2 as build requirements + minor fixes

[SpaceIm]

Specify library name and version: giflib/all

• I've read the guidelines for contributing.
• I've followed the PEP8 style guides for Python code in the recipes.
• I've used the latest Conan client version.
• I've tried at least one configuration locally with the
  conan-center hook activated.

I need giflib binaries to be available for Visual Studio, otherwise gdal will fail to build in CI of CCI when I'll submit it.

[conan-center-bot]

Some configurations of 'giflib/5.1.4' failed in build 1 (77d1b95059d0a813a424fc5162f65bdfd8d7e380):

• Windows x86_64, Release, Visual Studio 15, MD. Options: giflib:shared-True
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• Windows x86_64, Debug, Visual Studio 15, MDd. Options: giflib:shared-True
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[conan-center-bot]

All green in build 2 (132ecf0a95b985f759d2c3e23ce3dccaf568f8c0)! 😊

• giflib/5.1.4: Generated 82 packages. All logs here