Adding -fcontext-stack flag option to SlowComp. Compiles in under

a second now (fixes #5030) but needs large context stack.

testsuite/tests/ghc-regress/indexed-types/should_compile/all.T

@@ -174,4 +174,4 @@ test('T4981-V3', normal, compile, [''])
 
 test('T5002', normal, compile, [''])
 test('PushedInAsGivens', normal, compile, [''])
-test('SlowComp', normal, compile, [''])
\ No newline at end of file
+test('SlowComp', normal, compile, ['-fcontext-stack=300'])
\ No newline at end of file