Test that functions from `mingwex` are available

Ryan wrote these two minimizations, but they never got added to the test
suite.

See #23309, #23378

Co-Authored-By: Ben Gamari <bgamari.foss@gmail.com>
Co-Authored-By: Ryan Scott <ryan.gl.scott@gmail.com>

testsuite/tests/th/T23309.c

+#define _GNU_SOURCE 1
+#include <stdio.h>
+
+const char* foo(int e) {
+    static char s[256];
+    sprintf(s, "The value of e is: %u", e);
+    return s;
+}

testsuite/tests/th/T23309.hs

+{-# LANGUAGE TemplateHaskell #-}
+module T23309 where
+
+import Foreign.C.String
+import Language.Haskell.TH
+import System.IO
+
+import T23309A
+
+$(do runIO $ do
+       cstr <- c_foo 42
+       str <- peekCString cstr
+       hPutStrLn stderr str
+       hFlush stderr
+     return [])

testsuite/tests/th/T23309.stderr

+The value of e is: 42

testsuite/tests/th/T23309A.hs

+{-# LANGUAGE CPP #-}
+module T23309A (c_foo) where
+
+import Foreign.C.String
+import Foreign.C.Types
+
+#if defined(mingw32_HOST_OS)
+# if defined(i386_HOST_ARCH)
+#  define CALLCONV stdcall
+# elif defined(x86_64_HOST_ARCH)
+#  define CALLCONV ccall
+# else
+#  error Unknown mingw32 arch
+# endif
+#else
+# define CALLCONV ccall
+#endif
+
+foreign import CALLCONV unsafe "foo" c_foo :: CInt -> IO CString

testsuite/tests/th/T23378.hs

+{-# LANGUAGE TemplateHaskell #-}
+module T23378 where
+
+import Foreign.C.String
+import Language.Haskell.TH
+import System.IO
+
+import T23378A
+
+$(do runIO $ do
+       hPrint stderr isatty
+       hFlush stderr
+     return [])

testsuite/tests/th/T23378.stderr

+False

testsuite/tests/th/T23378A.hs

+{-# LANGUAGE CPP #-}
+module T23378A where
+
+import Foreign.C.Types
+import System.IO.Unsafe
+
+isatty :: Bool
+isatty =
+  unsafePerformIO (c_isatty 1) == 1
+{-# NOINLINE isatty #-}
+
+#if defined(mingw32_HOST_OS)
+# define SYM "_isatty"
+#else
+# define SYM "isatty"
+#endif
+
+foreign import ccall unsafe SYM
+  c_isatty :: CInt -> IO CInt

testsuite/tests/th/all.T

@@ -591,6 +591,8 @@ test('T23829_hasty', normal, compile_fail, [''])
 test('T23829_hasty_b', normal, compile_fail, [''])
 test('T23927', normal, compile_and_run, [''])
 test('T23954', normal, compile_and_run, [''])
+test('T23309', [extra_files(['T23309A.hs']), req_c], multimod_compile, ['T23309', '-v0 T23309.c -optc-fPIC'])
+test('T23378', [extra_files(['T23378A.hs']), js_skip], multimod_compile, ['T23378', '-v0'])
 test('T23962', normal, compile_and_run, [''])
 test('T23968', normal, compile_and_run, [''])
 test('T23971', normal, compile_and_run, [''])