[libunwind] Use placement new to avoid dependency C++ library

[phosek]

Summary

The rest of libunwind already uses placement new, these are the only
places where non-placement new is being used introducing undesirable
C++ library dependency.

[ldionne]

libunwind/src/libunwind.cpp

17

Can we get rid of this header then?

18

I think this header can go away regardless of the changes in this patch.

libunwind/src/libunwind.cpp

 //===--------------------------- libunwind.cpp ----------------------------===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
 //
 //  Implements unw_* functions from <libunwind.h>
 //
 //===----------------------------------------------------------------------===//
 
 #include <libunwind.h>
 
 #ifndef NDEBUG
 #include <cstdlib> // getenv
 #endif
 #include <new>
 #include <algorithm>
 
 #include "libunwind_ext.h"
 #include "config.h"
 
 #include <stdlib.h>
 
 
 #if !defined(__USING_SJLJ_EXCEPTIONS__)

 static bool is64bit(task_t task) {
   return false; // FIXME
 }
 
 /// Create an address_space object for use in examining another task.
 _LIBUNWIND_EXPORT unw_addr_space_t unw_create_addr_space_for_task(task_t task) {
 #if __i386__
   if (is64bit(task)) {
-    unw_addr_space_x86_64 *as = new unw_addr_space_x86_64(task);
+    unw_addr_space_x86_64 *as = malloc(sizeof(unw_addr_space_x86_64));
+    new (as) unw_addr_space_x86_64(task);
     as->taskPort = task;
     as->cpuType = CPU_TYPE_X86_64;
     //as->oas
   } else {
-    unw_addr_space_i386 *as = new unw_addr_space_i386(task);
+    unw_addr_space_i386 *as = malloc(sizeof(unw_addr_space_i386));
+    new (as) unw_addr_space_i386(task);
     as->taskPort = task;
     as->cpuType = CPU_TYPE_I386;
     //as->oas
   }
 #else
 // FIXME
 #endif
 }
 
 
 /// Delete an address_space object.
 _LIBUNWIND_EXPORT void unw_destroy_addr_space(unw_addr_space_t asp) {
   switch (asp->cpuType) {
 #if __i386__ || __x86_64__
   case CPU_TYPE_I386: {
     unw_addr_space_i386 *as = (unw_addr_space_i386 *)asp;
-    delete as;
+    as->~unw_addr_space_i386();
+    free(as);
   }
   break;
   case CPU_TYPE_X86_64: {
     unw_addr_space_x86_64 *as = (unw_addr_space_x86_64 *)asp;
-    delete as;
+    as->~unw_addr_space_x86_64();
+    free(as);
   }
   break;
 #endif
   case CPU_TYPE_POWERPC: {
     unw_addr_space_ppc *as = (unw_addr_space_ppc *)asp;
-    delete as;
+    as->~unw_addr_space_ppc();
+    free(as);
   }
   break;
   }
 }
 #endif // UNW_REMOTE
 
 
 /// Get value of specified register at cursor position in stack frame.