Use |noexcept| instead of an exception-specification in mozalloc.h

We are using |throw(std::bad_alloc)|, but dynamic exception specifications have been deprecated in C++11. The C++11 equivalent is |noexcept(false)|. This causes build warning spam when using newer compilers such as GCC 7.x.

memory/mozalloc/mozalloc.h

@@ -175,6 +175,12 @@ MFBT_API void* moz_xvalloc(size_t size)
  */
 #define MOZALLOC_THROW_IF_HAS_EXCEPTIONS
 #define MOZALLOC_THROW_BAD_ALLOC_IF_HAS_EXCEPTIONS
+#elif __cplusplus >= 201103
+/*
+ * C++11 has deprecated exception-specifications in favour of |noexcept|.
+ */
+#define MOZALLOC_THROW_IF_HAS_EXCEPTIONS noexcept(true)
+#define MOZALLOC_THROW_BAD_ALLOC_IF_HAS_EXCEPTIONS noexcept(false)
 #else
 #define MOZALLOC_THROW_IF_HAS_EXCEPTIONS throw()
 #define MOZALLOC_THROW_BAD_ALLOC_IF_HAS_EXCEPTIONS throw(std::bad_alloc)