[cxx-interop] Temporarily exclude CxxSetToCollection benchmark from the build

This is needed to unblock nightly toolchains, which are currently failing to build with an assertion:
```
swift-frontend: /home/build-user/build/buildbot_linux/llvm-linux-x86_64/tools/clang/include/clang/AST/TypeNodes.inc:79: TypeInfo clang::ASTContext::getTypeInfoImpl(const Type *) const: Assertion `!T->isDependentType() && "should not see dependent types here"' failed.
```

rdar://150067288

Author: egorzhdan

benchmark/cxx-source/CxxSetToCollection.swift

@@ -13,6 +13,8 @@
 // This is a benchmark that tracks how quickly Swift can convert a C++ set
 // to a Swift collection.
 
+/* FIXME: rdar://150067288
+
 import TestsUtils
 import CxxStdlibPerformance
 import Cxx
@@ -64,3 +66,5 @@ public func run_CxxSetOfU32_forEach(_ n: Int) {
     }
   }
 }
+
+*/

benchmark/cxx-source/CxxStringConversion.swift

@@ -10,6 +10,8 @@
 //
 //===----------------------------------------------------------------------===//
 
+/* FIXME: rdar://150067288
+
 import TestsUtils
 import CxxStdlibPerformance
 import CxxStdlib
@@ -58,3 +60,5 @@ public func run_cxxToSwift(_ n: Int) {
     blackHole(x)
   }
 }
+
+*/

benchmark/cxx-source/CxxVectorSum.swift

@@ -13,6 +13,8 @@
 // This is a benchmark that tracks how quickly Swift can sum up a C++ vector
 // as compared to the C++ implementation of such sum.
 
+/* FIXME: rdar://150067288
+
 import TestsUtils
 import CxxStdlibPerformance
 import Cxx
@@ -119,3 +121,5 @@ public func run_CxxVectorOfU32_Sum_Swift_Reduce(_ n: Int) {
     }
     blackHole(sum)
 }
+
+*/