So these can be used in other `.bzl` files.

I.e. when building a Haskell binary with `linkstatic = True`, then link
statically against Haskell and C library dependencies where possible.

GHC's default behaviour (following from the linker's behaviour) is to
prefer dynamic libraries over static libraries for C library
dependencies, even when linking statically against Haskell libraries.

By only passing static library versions (unless on static library is
available) of C library dependencies as inputs to the linking action,
the linker has no choice but to link statically.

Closes #580

Test that a Haskell binary compiled with `linkstatic = True`, will only
link to static library dependencies (where available), and that a
Haskell binary compiled with `linkstatic = False`, will link all its
library dependencies dynamically (where available).

The test cases assume that for each library dependency both a dynamic
and a static version are available, i.e. the default of `linkstatic =
False` for library dependencies.

Uses `haskell_test` in place of `haskell_binary` to ensure that the
resulting binaries can be executed without any runtime linker errors.

dbg mode enforces static linking in which case the test case for dynamic
linking will fail.

`objdump` is not available on the MacOS build. Furthermore, on MacOS
only direct library dependencies are listed under the shared library
dependencies. Also, on MacOS the dynamic library dependency listed in
the binary's header uses the library ID instead of the mangled library
path as on Linux.

This changes and simplifies the binary-linkstatic-flag tests to work on
both Linux and MacOS seemlessly.

First, we turn the indirect C library dependency into a direct
dependency.

Second, instead of checking for shared library dependencies, we directly
check for the `value` and `*HsLib_value_closure` symbols. In a
statically linked binary both those symbols will be defined directly in
the binary. In a dynamically linked binary both symbols will be listed
as undefined. The `nm` tool is available on both the Linux and MacOS
builds and can list all undefined symbols in the binary.