Add exception handling for new operator (#791)

The new operator in the snmalloc did not throw exceptions in the case of
allocation failure.  Moreover, it was not possible to override the
behaviour of the failure of the new operator using the
std::set_new_handler function.

This PR adds the necessary code to the snmalloc new operator to
throw std::bad_alloc when the allocation fails. It also allows the
std::set_new_handler function to be used to set a custom handler for
allocation failures.

src/test/func/miracle_ptr/miracle_ptr.cc

@@ -18,9 +18,27 @@ int main()
 #  include <atomic>
 #  include <iostream>
 #  include <memory>
+#  include <new>
 #  include <snmalloc/backend/globalconfig.h>
 #  include <snmalloc/snmalloc_core.h>
 
+// This code makes the delete overloads build with the correct noexcept spec.
+#  ifdef _WIN32
+#    ifdef __clang__
+#      define EXCEPTSPEC noexcept
+#    else
+#      define EXCEPTSPEC
+#    endif
+#  else
+#    ifdef _GLIBCXX_USE_NOEXCEPT
+#      define EXCEPTSPEC _GLIBCXX_USE_NOEXCEPT
+#    elif defined(_NOEXCEPT)
+#      define EXCEPTSPEC _NOEXCEPT
+#    else
+#      define EXCEPTSPEC
+#    endif
+#  endif
+
 namespace snmalloc
 {
   // Instantiate the allocator with a client meta data provider that uses an
@@ -170,12 +188,12 @@ void* operator new(size_t size)
   return snmalloc::miracle::malloc(size);
 }
 
-void operator delete(void* p)
+void operator delete(void* p) EXCEPTSPEC
 {
   snmalloc::miracle::free(p);
 }
 
-void operator delete(void* p, size_t)
+void operator delete(void* p, size_t) EXCEPTSPEC
 {
   snmalloc::miracle::free(p);
 }