rts: remove stable-names from hashtable upon free

This fixes #9078.

Signed-off-by: Austin Seipp <austin@well-typed.com>

rts/Stable.c

@@ -246,6 +246,7 @@ STATIC_INLINE void
 freeSnEntry(snEntry *sn)
 {
   ASSERT(sn->sn_obj == NULL);
+  removeHashTable(addrToStableHash, (W_)sn->old, NULL);
   sn->addr = (P_)stable_name_free;
   stable_name_free = sn;
 }

testsuite/tests/rts/T9078.hs

+module Main where
+
+import Control.Monad
+import System.Mem.StableName
+
+main :: IO ()
+main = replicateM_ 500000 (makeStableName foo)
+
+foo :: Int
+foo = 1

testsuite/tests/rts/T9078.stderr

+cap 0: initialised
+cap 0: shutting down

testsuite/tests/rts/all.T

@@ -227,3 +227,6 @@ test('T8124', [ only_ways(threaded_ways), omit_ways(['ghci']),
 # The ghci way gets confused by the RTS options
 test('T9045', [ omit_ways(['ghci']), extra_run_opts('10000 +RTS -A8k -RTS') ], compile_and_run, [''])
 
+# I couldn't reproduce 9078 with the -threaded runtime, but could easily
+# with the non-threaded one.
+test('T9078', [ omit_ways(threaded_ways) ], compile_and_run, ['-with-rtsopts="-DS" -debug'])