Improve and test diagnostic for compiler version component being out-of-range

The compiler diagnostic here wasn't great; improve it.

Author: DougGregor

Sources/SwiftIfConfig/IfConfigDiagnostic.swift

@@ -60,10 +60,8 @@ enum IfConfigDiagnostic: Error, CustomStringConvertible {
     case .emptyVersionComponent(syntax: _):
       return "found empty version component"
 
-    case .compilerVersionOutOfRange(value: _, upperLimit: let upperLimit, syntax: _):
-      // FIXME: This matches the C++ implementation, but it would be more useful to
-      // provide the actual value as-written and avoid the mathy [0, N] syntax.
-      return "compiler version component out of range: must be in [0, \(upperLimit)]"
+    case .compilerVersionOutOfRange(value: let value, upperLimit: let upperLimit, syntax: _):
+      return "compiler version component '\(value)' is not in the allowed range 0...\(upperLimit)"
 
     case .compilerVersionSecondComponentNotWildcard(syntax: _):
       return "the second version component is not used for comparison in legacy compiler versions"

Tests/SwiftIfConfigTest/EvaluateTests.swift

@@ -323,6 +323,19 @@ public class EvaluateTests: XCTestCase {
         )
       ]
     )
+
+    assertIfConfig(
+      #"_compiler_version("5009.*.1000")"#,
+      .unparsed,
+      diagnostics: [
+        DiagnosticSpec(
+          message: "compiler version component '1000' is not in the allowed range 0...999",
+          line: 1,
+          column: 20,
+          severity: .error
+        )
+      ]
+    )
   }
 
   func testCanImport() throws {