CVE-2019-14876

In the __lshift function of the newlib libc library, all versions prior to
3.3.0 (see newlib/libc/stdlib/mprec.c), Balloc is used to allocate a big
integer, however no check is performed to verify if the allocation
succeeded or not. The access to b1 will trigger a null pointer dereference
bug in case of a memory allocation failure.