it is possible, but the usual way to do this is to define a separate package called "Csomething", where you simply prefix the name of the C library with C capital and post it on Github. Package C should consist only of an empty file Package.swiftand module.modulemap. In module.modulemapyou indicate where the C headers are:
module CPackage [system] {
header "/usr/local/include/myheader.h"
link "libraryname"
export *
}
, CPackage, :
.Package(url: "https://github.com/aleph7/CHDF5.git", majorVersion: 1)
import CPackage
https://github.com/aleph7/CHDF5 C