Add explicit (void) cast to unused unique_ptr::release() results

Summary:
This patch adds explicit `(void)` casts to discarded `release()` calls to suppress -Wunused-result.

This patch fixes *all* warnings are generated as a result of [applying `[[nodiscard]]`  within libc++](https://reviews.llvm.org/D26596).
Similar fixes were applied to Clang in r286796.

Reviewers: chandlerc, dberris

Subscribers: llvm-commits

Differential Revision: https://reviews.llvm.org/D26598

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@286797 91177308-0d34-0410-b5e6-96231b3b80d8

include/llvm/DebugInfo/PDB/IPDBSession.h

@@ -40,7 +40,7 @@ class IPDBSession {
     T *ConcreteSymbol = dyn_cast<T>(Symbol.get());
     if (!ConcreteSymbol)
       return nullptr;
-    Symbol.release();
+    (void)Symbol.release();
     return std::unique_ptr<T>(ConcreteSymbol);
   }
 

lib/Bitcode/Reader/BitReader.cpp

@@ -84,7 +84,9 @@ LLVMBool LLVMGetBitcodeModuleInContext(LLVMContextRef ContextRef,
   std::unique_ptr<MemoryBuffer> Owner(unwrap(MemBuf));
   Expected<std::unique_ptr<Module>> ModuleOrErr =
       getOwningLazyBitcodeModule(std::move(Owner), Ctx);
-  Owner.release();
+  // Release the buffer if we didn't take ownership of it since we never owned
+  // it anyway.
+  (void)Owner.release();
 
   if (Error Err = ModuleOrErr.takeError()) {
     std::string Message;