binfmt_flat: Fix corruption when not offsetting data start

In the Linux kernel, the following vulnerability has been resolved: binfmt_flat: Fix corruption when not offsetting data start Commit 04d82a6d0881 ("binfmt_flat: allow not offsetting data start") introduced a RISC-V specific variant of the FLAT format which does not allocate any space for the (obsolete) array of shared library pointers. However, it did not disable the code which initializes the array, resulting in the corruption of sizeof(long) bytes before the DATA segment, generally the end of the TEXT segment. Introduce MAX_SHARED_LIBS_UPDATE which depends on the state of CONFIG_BINFMT_FLAT_NO_DATA_START_OFFSET to guard the initialization of the shared library pointer region so that it will only be initialized if space is reserved for it.