misc: Updates for gcc7.2 for x86

GCC 7.2 is much stricter than previous GCC versions. The following changes
are needed:

* There is now a warning if there is an implicit fallthrough between two
  case statments. C++17 adds the [[fallthrough]]; declaration. However,
  to support non C++17 standards (i.e., C++11), we use M5_FALLTHROUGH.
  M5_FALLTHROUGH checks for [[fallthrough]] compliant C++17 compiler and
  if that doesn't exist, it defaults to nothing (no older compilers
  generate warnings).
* The above resulted in a couple of bugs that were found. This is noted
  in the review request on gerrit.
* throw() for dynamic exception specification is deprecated
* There were a couple of new uninitialized variable warnings
* Can no longer perform bitwise operations on a bool.
* Must now include <functional> for std::function
* Compiler bug for void* lambda. Changed to auto as work around. See
  https://gcc.gnu.org/bugzilla/show_bug.cgi?id=82878

Change-Id: I5d4c782a4e133fa4cdb119e35d9aff68c6e2958e
Signed-off-by: Jason Lowe-Power <jason@lowepower.com>
Reviewed-on: https://gem5-review.googlesource.com/5802
Reviewed-by: Gabe Black <gabeblack@google.com>

src/sim/fd_array.cc

@@ -131,8 +131,7 @@ FDArray::restoreFileOffsets()
      * possible to guarantee that the simulation will proceed as it should
      * have in the same way that it would have proceeded sans checkpoints.
      */
-    void (*seek)(std::shared_ptr<FileFDEntry>)
-        = [] (std::shared_ptr<FileFDEntry> ffd)
+    auto seek = [] (std::shared_ptr<FileFDEntry> ffd)
     {
         if (lseek(ffd->getSimFD(), ffd->getFileOffset(), SEEK_SET) < 0)
             fatal("Unable to seek to location in %s", ffd->getFileName());