Add some simple meta-tests for the handling of filecheck flags

tests/codegen/meta-filecheck/check-prefix.rs

@@ -0,0 +1,4 @@
+// Simple test that uses the default CHECK prefix and should always succeed.
+
+// CHECK: main
+fn main() {}

tests/codegen/meta-filecheck/msvc-prefix-bad.rs

@@ -0,0 +1,7 @@
+// This is exactly like `msvc-prefix-good.rs`, except that it should always fail.
+
+//@ should-fail
+
+// MSVC: text that should not match
+// NONMSVC: text that should not match
+fn main() {}

tests/codegen/meta-filecheck/msvc-prefix-good.rs

@@ -0,0 +1,7 @@
+// One of MSVC or NONMSVC should always be defined, so this test should pass.
+
+// (one of these should always be present)
+
+// MSVC: main
+// NONMSVC: main
+fn main() {}

tests/codegen/meta-filecheck/no-directives.rs

@@ -0,0 +1,5 @@
+// A test that doesn't include any filecheck directives should fail.
+
+//@ should-fail
+
+fn main() {}

tests/codegen/meta-filecheck/revision-prefix.rs

@@ -0,0 +1,8 @@
+// The current revision name is registered as a filecheck prefix.
+
+//@ revisions: GOOD BAD
+//@ [BAD] should-fail
+
+// GOOD: main
+// BAD: text that should not match
+fn main() {}