Constant-folding lacking for `timesInt2#`

timesInt2# lacks constant folding. It's an issue when we try to inline ghc-bignum operations, e.g.:

--- "/builds/hsyl20/ghc/tmp/ghctest-sbdktbdc/test   spaces/testsuite/tests/lib/integer/integerConstantFolding.run/integerConstantFolding.stdout.normalised"	2021-09-13 09:32:38.597998758 +0000
+++ "/builds/hsyl20/ghc/tmp/ghctest-sbdktbdc/test   spaces/testsuite/tests/lib/integer/integerConstantFolding.run/integerConstantFolding.run.stdout.normalised"	2021-09-13 09:32:38.597998758 +0000
@@ -1,3 +1,16 @@
+Unfolded values found
+  = case GHC.Prim.timesInt2# 100005# 6832# of

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