Bug 1747756 - Move Windows system libraries from LIBS to moz.build. r=firefox-build-system-reviewers,mhentges

While mingw builds don't require user32 and advapi32 explicitly, it doesn't
hurt for them to be there (and they're required for clang-cl build).
Likewise, while clang-builds don't require uuid and userenv explicitly
because they're pulled in via #pragmas in the source code, mingw doesn't
support those #pragmas and needs them explicitly, which doesn't hurt the
clang-cl builds.

Differential Revision: https://phabricator.services.mozilla.com/D134737