Enable the >=version syntax for #if _compiler_version

In addition to the string-literal form, this compilation conditional
handles the same version check syntax as `#if swift` and `#if compiler`.

Author: DougGregor

Sources/SwiftIfConfig/IfConfigEvaluation.swift

@@ -334,13 +334,7 @@ func evaluateIfConfig(
         let segment = stringLiteral.segments.first,
         case .stringSegment(let stringSegment) = segment
       else {
-        return recordError(
-          .requiresUnlabeledArgument(
-            name: "_compiler_version",
-            role: "version",
-            syntax: ExprSyntax(call)
-          )
-        )
+        return doVersionComparisonCheck(configuration.compilerVersion)
       }
 
       let versionString = stringSegment.content.text

Tests/SwiftIfConfigTest/EvaluateTests.swift

@@ -193,6 +193,8 @@ public class EvaluateTests: XCTestCase {
     assertIfConfig(#"_compiler_version("5009.*.1")"#, .active)
     assertIfConfig(#"_compiler_version("5009.*.3.2.3")"#, .unparsed)
     assertIfConfig(#"_compiler_version("5010.*.0")"#, .unparsed)
+    assertIfConfig("_compiler_version(>=5.8)", .active)
+    assertIfConfig("_compiler_version(>=12.0)", .unparsed)
     assertIfConfig("compiler(>=5.10) && 3.14159", .unparsed)
     assertIfConfig(
       "compiler(>=5.10) || 3.14159",