bson.modulemap

module CLibbson [system] {
    header "/usr/local/include/libbson-1.0/bson.h"
    link "bson-1.0"
    export *
}

err.sh

$> swift build
Compiling Swift Module 'test' (1 sources)
<module-includes>:1:9: note: in file included from <module-includes>:1:
#import "/usr/local/include/libmongoc-1.0/mongoc.h"
        ^
/usr/local/include/libmongoc-1.0/mongoc.h:22:10: error: 'bson.h' file not found
#include <bson.h>
         ^
/Users/dan/Downloads/test/main.swift:1:8: error: could not build Objective-C module 'CMongoC'
import CMongoC
       ^
<unknown>:0: error: build had 1 command failures
swift-build: exit(1): ["/Library/Developer/Toolchains/swift-2.2-SNAPSHOT-2015-12-01-a.xctoolchain/usr/bin/swift-build-tool", "-f", "/Users/dan/Downloads/test/.build/debug/test.o/llbuild.yaml"]

mongoc.modulemap

module CMongoC [system] {
    header "/usr/local/include/libmongoc-1.0/mongoc.h"
    link "mongoc-1.0"
    export *
}