[Module interface] Ensure that we keep #ifs for compiler workarounds.

Fixes rdar://76236364.

Author: DougGregor

lib/AST/InlinableText.cpp

@@ -55,6 +55,15 @@ class IsFeatureCheck : public ASTWalker {
         foundFeature = true;
     }
 
+    if (auto call = dyn_cast<CallExpr>(expr)) {
+      if (auto unresolved = dyn_cast<UnresolvedDeclRefExpr>(call->getFn())) {
+        StringRef userFacing = unresolved->getName().getBaseName()
+            .userFacingName();
+        if (userFacing == "compiler" || userFacing == "_compiler_version")
+          foundFeature = true;
+      }
+    }
+
     return { !foundFeature, expr };
   }
 };
@@ -128,10 +137,9 @@ struct ExtractInactiveRanges : public ASTWalker {
       return false;
     }
 
-    // If the clause is checking for a particular feature with $, keep
-    // the whole thing.
+    // If the clause is checking for a particular feature with $ or a compiler
+    // version, keep the whole thing.
     if (anyClauseIsFeatureCheck(icd->getClauses())) {
-      addRange(start, end);
       return false;
     }
 

test/ModuleInterface/if-configs.swift

@@ -109,3 +109,19 @@ public func hasClosureDefaultArgWithSinglePoundIf(_ x: () -> Void = {
   #endif
 }) {
 }
+
+// CHECK: func hasIfCompilerCheck
+// CHECK:      #if compiler(>=5.3)
+// CHECK-NEXT:   return true
+// CHECK-NEXT: #else
+// CHECK-NEXT:   return false
+// CHECK-NEXT: #endif
+@_alwaysEmitIntoClient
+public func hasIfCompilerCheck(_ x: () -> Bool = {
+#if compiler(>=5.3)
+  return true
+#else
+  return false
+#endif
+  }) {
+}