Add JEMALLOC_CXX_THROW to the memalign() function prototype, in order to match glibc and avoid compilation errors when including both jemalloc/jemalloc.h and malloc.h in C++ code. This change was unintentionally omitted from ae93d6bf364e9db9f9ee69c3e5f9df110d8685a4 (Avoid function prototype incompatibilities.).