Testsuite: mark T6037 expect_fail on Windows (#6037)

testsuite/tests/driver/Makefile

@@ -551,8 +551,8 @@ T7563:
 	-"$(TEST_HC)" $(TEST_HC_OPTS_NO_RECOMP) -C T7563.hs
 
 # Below we set LC_ALL=C to request standard ASCII output in the resulting error
-# messages. Unfortunately, Mac OS X still uses a Unicode encoding even with
-# LC_ALL=C, so we expect these tests to fail there.
+# messages. Unfortunately, Mac OS X and Windows still use a Unicode encoding
+# even with LC_ALL=C, so we expect these tests to fail there.
 
 .PHONY: T6037
 T6037:

testsuite/tests/driver/all.T

@@ -382,7 +382,10 @@ test('T7060',
 test('T7130', normal, compile_fail, ['-fflul-laziness'])
 test('T7563', when(unregisterised(), skip), run_command,
      ['$MAKE -s --no-print-directory T7563'])
-test('T6037', normal, run_command,
+test('T6037',
+     # The testsuite doesn't know how to set a non-Unicode locale on Windows or Mac OS X
+     [when(opsys('mingw32'), expect_fail), when(opsys('darwin'), expect_fail)],
+     run_command,
      ['$MAKE -s --no-print-directory T6037'])
 test('T2507',
      # The testsuite doesn't know how to set a non-Unicode locale on Windows or Mac OS X