Normalize revisions used for filecheck directives

Typically, filecheck prefixes will be uppercase (always true) and start
with `CHECK-` (almost always true). Currently we allow using revision
names as filecheck directives, but they are passed directly.  That means
that our directives are exactly what the revision name is, in the same
case, so they only look like filecheck directives if the revision name
is uppercase (usually they are lowercase).

Update this so that we always uppercase revision names and prefix them
with `CHECK-` when used as directives. This is better for consistency,
makes it easier to identify directives in the tests, and has the nice
side effect that some editors will make the directive stand out by
highlighting it (which currently happens for most directives, just not
those from revisions).

Author: tgross35

src/tools/compiletest/src/runtest.rs

@@ -2608,13 +2608,14 @@ impl<'test> TestCx<'test> {
         // Because we use custom prefixes, we also have to register the default prefix.
         filecheck.arg("--check-prefix=CHECK");
 
-        // Some tests use the current revision name as a check prefix.
+        // The current revision name can also be used as a check prefix
         if let Some(rev) = self.revision {
-            filecheck.arg("--check-prefix").arg(rev);
+            filecheck.arg(format!("--check-prefix=CHECK-{}", rev.to_uppercase()));
         }
 
         // Some tests also expect either the MSVC or NONMSVC prefix to be defined.
-        let msvc_or_not = if self.config.target.contains("msvc") { "MSVC" } else { "NONMSVC" };
+        let msvc_or_not =
+            if self.config.target.contains("msvc") { "CHECK-MSVC" } else { "CHECK-NONMSVC" };
         filecheck.arg("--check-prefix").arg(msvc_or_not);
 
         // The filecheck tool normally fails if a prefix is defined but not used.