Uncomment the instance signatures, to activate the test
Revert "Add purgeObj() to remove the symbol table entries for an object"

This reverts commit 9e6e4796437a7fc23e83605a45db9b2663570123.

I reverted it because one of these two patches
  9e6e4796437a7fc23e83605a45db9b2663570123 Add purgeObj()
  b5e8b3b162b3ff15ae6caf1afc659565365f54a8 Make the linker API thread-safe

causes a seg-fault on Windows.  The seg-fault happens immediately
the linker is invoked, in ghci or in Template Haskell.

I believe that it is the "linker API thread-safe" commit that causes
the seg-fault; it happens even if the "purgeObj" commit alone is
reverted.  But since the two patches mess with the same code, to
revert the "linker API" patch I had revert both.
Revert "Make the linker API thread-safe"

This reverts commit b5e8b3b162b3ff15ae6caf1afc659565365f54a8.

I reverted it because one of these two patches
  9e6e4796437a7fc23e83605a45db9b2663570123 Add purgeObj()
  b5e8b3b162b3ff15ae6caf1afc659565365f54a8 Make the linker API thread-safe

causes a seg-fault on Windows.  The seg-fault happens immediately
the linker is invoked, in ghci or in Template Haskell.

I believe that it is the "linker API thread-safe" commit that causes
the seg-fault; it happens even if the "purgeObj" commit alone is
reverted.  But since the two patches mess with the same code, to
revert the "linker API" patch I had revert both.