add nothrow attributes to jemalloc non-standard API declarations.
add nothrow attributes to jemalloc non-standard API declarations.

Summary: According to https://github.com/jemalloc/jemalloc/issues/237 and https://fburl.com/aeia78qk, `__attribute__((nothrow))` is added to jemalloc API functions to be in compatible with `stdlib.h`.

Reviewed By: yfeldblum

Differential Revision: D17679036

fbshipit-source-id: 525a076f19719d2406c0dce92ca814f5f5011497

facebook/folly,facebook/folly,facebook/folly,facebook/folly,facebook/folly