Makefile.am: Fix wrong -dep-suffix for GHC 7.8

This works around https://ghc.haskell.org/trac/ghc/ticket/9749:

GHC 7.8 (undocumentedly) changed the way in which ghc -M generated
object file dependencies, lacking the underscore that older versions
added automatically to the file names.
It also requires a -dep-suffix for the plain object file (.o).

This commit detects GHC 7.6 and older (7.7 is development only, has no
release and is treated equal to 7.8), and adjusts the -M invocation
appropriately for newer GHC versions.

Signed-off-by: Niklas Hambuechen <niklash@google.com>
Fix compiler invocation for GHC >= 7.8

GHC 7.8 switched to dynamic linking being used for ghci, which requires
that .so file are being built for modules that are loaded for TH.

For this reason, GHC >= 7.8 has a -dynamic-too flag, which we now use.

However, -dynamic-too must not be enabled for profiling builds,
which is why this commit introduces a HFLAGS_NOPROF variable
(currently only containing -dynamic-too) that must be passed to
all GHC invocations that are not creating profiling output.

Signed-off-by: Niklas Hambuechen <niklash@google.com>