[AutoDiff] [SR-14240] Align name mangling for Clang-imported declarations (#38850)

* Adding fix for handling Clang-imported names, along with test case.

* Correct EOL.

Author: BradLarson

lib/AST/ASTMangler.cpp

@@ -459,6 +459,14 @@ void ASTMangler::beginManglingWithAutoDiffOriginalFunction(
     appendOperator(attr->Name);
     return;
   }
+  // For imported Clang declarations, use the Clang name in order to match how
+  // DifferentiationMangler handles these.
+  auto clangDecl = getClangDeclForMangling(afd);
+  if (clangDecl) {
+    beginManglingWithoutPrefix();
+    appendOperator(clangDecl->getName());
+    return;
+  }
   beginMangling();
   if (auto *cd = dyn_cast<ConstructorDecl>(afd))
     appendConstructorEntity(cd, /*isAllocating*/ !cd->isConvenienceInit());

test/AutoDiff/compiler_crashers_fixed/sr14240-symbol-in-ir-file-not-tbd-file.swift

@@ -0,0 +1,24 @@
+// RUN: %target-run-simple-swift(-Xfrontend -requirement-machine=off)
+
+// SR-14240: Error: symbol 'powTJfSSpSr' (powTJfSSpSr) is in generated IR file,
+// but not in TBD file.
+
+import _Differentiation
+
+#if canImport(Darwin)
+  import Darwin
+#elseif canImport(Glibc)
+  import Glibc
+#elseif os(Windows)
+  import CRT
+#else
+#error("Unsupported platform")
+#endif
+
+@inlinable
+@derivative(of: pow)
+func powVJP(
+  _ base: Double, _ exponent: Double
+) -> (value: Double, pullback: (Double) -> (Double, Double)) {
+  fatalError()
+}