SILOptimizer: Disable invalid passes in C++-only compiler

The SimplifyCFG and LoopRotate passes result in verification failures
when built in a compiler that is not built with Swift sources enabled.

Fixes: rdar://146357242

cmake/modules/AddSwift.cmake

@@ -324,6 +324,9 @@ function(_add_host_variant_c_compile_flags target)
     target_compile_definitions(${target} PRIVATE
       $<$<COMPILE_LANGUAGE:C,CXX,OBJC,OBJCXX>:_LARGEFILE_SOURCE _FILE_OFFSET_BITS=64>)
   endif()
+
+  target_compile_definitions(${target} PRIVATE
+    $<$<AND:$<COMPILE_LANGUAGE:C,CXX,OBJC,OBJCXX>,$<BOOL:${SWIFT_ENABLE_SWIFT_IN_SWIFT}>>:SWIFT_ENABLE_SWIFT_IN_SWIFT>)
 endfunction()
 
 function(_add_host_variant_link_flags target)

lib/SILOptimizer/LoopTransforms/LoopRotate.cpp

@@ -485,6 +485,12 @@ namespace {
 class LoopRotation : public SILFunctionTransform {
 
   void run() override {
+#ifndef SWIFT_ENABLE_SWIFT_IN_SWIFT
+    // This pass results in verification failures when Swift sources are not
+    // enabled.
+    LLVM_DEBUG(llvm::dbgs() << "Loop Rotate disabled in C++-only Swift compiler\n");
+    return;
+#endif // !SWIFT_ENABLE_SWIFT_IN_SWIFT
     SILFunction *f = getFunction();
     SILLoopAnalysis *loopAnalysis = PM->getAnalysis<SILLoopAnalysis>();
     DominanceAnalysis *domAnalysis = PM->getAnalysis<DominanceAnalysis>();

lib/SILOptimizer/Transforms/SimplifyCFG.cpp

@@ -3317,6 +3317,12 @@ static bool splitBBArguments(SILFunction &Fn) {
 }
 
 bool SimplifyCFG::run() {
+#ifndef SWIFT_ENABLE_SWIFT_IN_SWIFT
+  // This pass results in verification failures when Swift sources are not
+  // enabled.
+  LLVM_DEBUG(llvm::dbgs() << "SimplifyCFG disabled in C++-only Swift compiler\n");
+  return false;
+#endif //!SWIFT_ENABLE_SWIFT_IN_SWIFT
   LLVM_DEBUG(llvm::dbgs() << "### Run SimplifyCFG on " << Fn.getName() << '\n');
 
   // Disable some expensive optimizations if the function is huge.