crunch macos noexcept

```
clang --version
Apple LLVM version 10.0.1 (clang-1001.0.46.4)
Target: x86_64-apple-darwin18.7.0
Thread model: posix
InstalledDir: /Library/Developer/CommandLineTools/usr/bin
```

```
diff --git a/crnlib/crn_threading_pthreads.h b/crnlib/crn_threading_pthreads.h
index 50f3fb0..a2d7f1f 100644
--- a/crnlib/crn_threading_pthreads.h
+++ b/crnlib/crn_threading_pthreads.h
@@ -174,7 +174,7 @@ class task_pool {
   class executable_task {
    public:
     virtual void execute_task(uint64 data, void* pData_ptr) = 0;
-    virtual ~executable_task( void ) = default;
+    virtual ~executable_task( void ) noexcept = default;
   };

   // It's the caller's responsibility to delete pObj within the execute_task() method, if needed!
@@ -250,7 +250,7 @@ class object_task : public task_pool::executable_task {
         m_flags(flags) {
     CRNLIB_ASSERT(pObject && pMethod);
   }
-  virtual ~object_task( void ) = default;
+  virtual ~object_task( void ) noexcept = default;

   void init(T* pObject, object_method_ptr pMethod, uint flags = cObjectTaskFlagDefault) {
     CRNLIB_ASSERT(pObject && pMethod);
```

```
crunch/crnlib/crn_threading_pthreads.h:177:37: error: expected ';' at end of
      declaration list
    virtual ~executable_task( void ) noexcept = default;
                                    ^
                                    ;
crunch/crnlib/crn_threading_pthreads.h:253:31: error: expected ';' at end of
      declaration list
  virtual ~object_task( void ) noexcept = default;
                              ^
                              ;
```