Fix “redefinition of module ‘X’” for xcframeworks with module maps

Fixes a regression in 4.201.0-rc.1 where depending on an xcframework that ships a module.modulemap caused the compiler to fail with “redefinition of module ‘X’”. The library header search path logic now skips the Headers folder of any xcframework that has module maps, since Xcode’s ProcessXCFramework already exposes them through the include/ copy. xcframeworks without module maps continue to have their headers added, so the cached Swift and library products support is unaffected.