Add tests for #15617.

Avoid a similar regression in the future.

testsuite/tests/ghc-e/should_run/Makefile

@@ -45,3 +45,9 @@ T9905b:
 # Ensure that ghc -e does not output extra messages about GHCi configuration files
 T11478:
 	'$(TEST_HC)' $(TEST_HC_OPTS) -ignore-dot-ghci -ghci-script T11478.script -e 3
+
+T15617a:
+	'$(TEST_HC)' $(TEST_HC_OPTS) -ignore-dot-ghci -fobject-code -O2 -e "let a = show 5 in a"
+
+T15617b:
+	'$(TEST_HC)' $(TEST_HC_OPTS) -ignore-dot-ghci -fobject-code -O2 -e "a = show 5"

testsuite/tests/ghc-e/should_run/T15617a.stdout

+"5"

testsuite/tests/ghc-e/should_run/all.T

@@ -16,3 +16,5 @@ test('T9086', req_interp, makefile_test, ['T9086'])
 test('T9905', req_interp, makefile_test, ['T9905'])
 test('T9905b', req_interp, makefile_test, ['T9905b'])
 test('T11478', req_interp, makefile_test, ['T11478'])
+test('T15617a', req_interp, makefile_test, ['T15617a'])
+test('T15617b', req_interp, makefile_test, ['T15617b'])