discussion on cIncludeDir, cCompile, cImport

[timotheecour]

i think cIncludeDir("include”) is being mis-used; IMO cCompile and cImport should be given actual paths where sources (h and c) live, and cIncludeDir would only be used to resolve where to find bar.h if a h or c file contains #include bar.h

Note: further discussed here: https://gitter.im/nimgen/Lobby?at=5bf5f541a115c91ef77149b9