Add test for haskell#7423

i.e. Do not warn on -O2 if under off-by-default package configuration
flag conditional.

cabal-testsuite/PackageTests/Check/ConfiguredPackage/GHCOptions/NoWarnFlag/cabal.out

@@ -0,0 +1,2 @@
+# cabal check
+No errors or warnings could be found in the package.

cabal-testsuite/PackageTests/Check/ConfiguredPackage/GHCOptions/NoWarnFlag/cabal.test.hs

@@ -0,0 +1,4 @@
+import Test.Cabal.Prelude
+
+-- Do not output warning when an -O2 is behind a cabal flag.
+main = cabalTest $ cabal "check" []

cabal-testsuite/PackageTests/Check/ConfiguredPackage/GHCOptions/NoWarnFlag/pkg.cabal

@@ -0,0 +1,18 @@
+cabal-version: 2.2
+name: pkg
+version: 0
+category: example
+maintainer: [email protected]
+synopsis: synopsys
+description: description
+license: GPL-3.0-or-later
+
+flag force-O2
+  default: False
+  manual: True
+
+library
+  exposed-modules:      Foo
+  default-language:     Haskell2010
+  if flag(force-O2)
+    ghc-options:        -O2

cabal-testsuite/PackageTests/Check/ConfiguredPackage/GHCOptions/NoWarnFlagOut/cabal.out

@@ -0,0 +1,4 @@
+# cabal check
+Warning: These warnings may cause trouble when distributing the package:
+Warning: 'ghc-options: -O2' is rarely needed. Check that it is giving a real benefit and not just imposing longer compile times on your users.
+

cabal-testsuite/PackageTests/Check/ConfiguredPackage/GHCOptions/NoWarnFlagOut/cabal.test.hs

@@ -0,0 +1,4 @@
+import Test.Cabal.Prelude
+
+-- Output warning when an -O2 outside a cabal flag, along with one inside.
+main = cabalTest $ cabal "check" []

cabal-testsuite/PackageTests/Check/ConfiguredPackage/GHCOptions/NoWarnFlagOut/pkg.cabal

@@ -0,0 +1,19 @@
+cabal-version: 2.2
+name: pkg
+version: 0
+category: example
+maintainer: [email protected]
+synopsis: synopsys
+description: description
+license: GPL-3.0-or-later
+
+flag force-O2
+  default: False
+  manual: True
+
+library
+  exposed-modules:      Foo
+  default-language:     Haskell2010
+  ghc-options:          -O2
+  if flag(force-O2)
+    ghc-options:        -O2