This allows parallel compilation of all targets, including the Haskell
object files. While re-starting GHC for every Haskell source almost
doubles the total CPU time, allowing it run in parallel at the end cuts
down the wall-clock time to half.

Haskell targets are split into two: main ones and testing ones.
The testing targets (starting with "test/") are build with coverage
automatically. Therefore the testing object and interface files have
different extensions (this also allows their parallel compilation).

GHC is now used to produce a separate Makefile.ghc with all
dependencies. This is then included and used for compiling each object
file separately.

Note that the inclusion + generation of Makefile.ghc is turned off when
calling clean/ganeti/distclean. For some reason, Makefile infinitely
recurses when calling "make ganeti", if it includes Makefile.ghc. But
since using ifneq/endif in Makefile.am conflicts with Automake, it was
necessary to put the snippet into an Automake variable and substitute it
into the resulting Makefile.

Signed-off-by: Petr Pudlak <pudlak@google.com>
Reviewed-by: Klaus Aehlig <aehlig@google.com>