hsc2hs doesn't use defines from its cc_library dependencies

[iphydf]

cc_library(
    name = "cbits",
    # XXX: Can't do this yet, because I don't know how to make HsFFI.h visible
    # to this library (needs some dep from ghc).
    #srcs = glob(["cbits/*.c"]),
    hdrs = [
        "include/HsNet.h",
        "include/HsNetworkConfig.h",
    ],
    includes = ["include"],
    defines = ["_GNU_SOURCE"],  # <--- **HERE**
)

haskell_library(
    name = "network",
    srcs = [
        "Network.hs",
        "Network/BSD.hsc",
        "Network/Socket.hsc",
        "Network/Socket/ByteString.hsc",
        "Network/Socket/ByteString/IOVec.hsc",
        "Network/Socket/ByteString/Internal.hs",
        "Network/Socket/ByteString/Lazy.hs",
        "Network/Socket/ByteString/Lazy/Posix.hs",
        "Network/Socket/ByteString/MsgHdr.hsc",
        "Network/Socket/Internal.hsc",
        "Network/Socket/Types.hsc",
    ],
    compiler_flags = [
        "-XCPP",
        # XXX: Hack because for some reason it doesn't end up being defined.
        "-DCALLCONV=ccall",
    ],
    prebuilt_dependencies = [
        "base",
        "bytestring",
    ],
    visibility = ["//visibility:public"],
    deps = [":cbits"],  # <--- **USED HERE**
)

[mrkkrp]

I tried to make it work but it looks like it's blocked on bazelbuild/bazel#4370.

[iphydf]

This isn't blocking me, so I'm happy for this to be P3 (or whatever is the lowest).

[ruuda]

This now works fine for me with rules_haskell a7ed281. It did not work with v0.5.

[mboes]

Confirmed that the above BUILD file now works.