Open source builds fail for some Arm CPUs about mysql-5.6

[mdcallag]

The error:

In file included from /home/mcallaghan/fbmysql-56/storage/rocksdb/./ha_rocksdb.h:32,
                 from /home/mcallaghan/fbmysql-56/storage/rocksdb/ha_rocksdb.cc:24:
/home/mcallaghan/fbmysql-56/include/my_checksum.h: In instantiation of ‘uint32_t mycrc32::PunnedCrc32(uint32_t, const unsigned char*, size_t) [with PT = long unsigned int; uint32
_t = unsigned int; size_t = long unsigned int]’:
/home/mcallaghan/fbmysql-56/include/my_checksum.h:118:47:   required from here
/home/mcallaghan/fbmysql-56/include/my_checksum.h:93:11: error: ‘memcpy’ was not declared in this scope, and no declarations were found by argument-dependent lookup at the point of instantiation [-fpermissive]
   93 |     memcpy(&pv, buf, sizeof(PT));
      |     ~~~~~~^~~~~~~~~~~~~~~~~~~~~~
In file included from /usr/include/features.h:486,
                 from /usr/include/aarch64-linux-gnu/c++/11/bits/os_defines.h:39,
                 from /usr/include/aarch64-linux-gnu/c++/11/bits/c++config.h:586,
                 from /usr/include/c++/11/bits/stl_algobase.h:59,
                 from /usr/include/c++/11/deque:60,
                 from /home/mcallaghan/fbmysql-56/storage/rocksdb/./ha_rocksdb.h:23,
                 from /home/mcallaghan/fbmysql-56/storage/rocksdb/ha_rocksdb.cc:24:
/usr/include/aarch64-linux-gnu/bits/string_fortified.h:26:1: note: ‘void* memcpy(void*, const void*, size_t)’ declared here, later in the translation unit
   26 | __NTH (memcpy (void *__restrict __dest, const void *__restrict __src,
      | ^~~~~
In file included from /home/mcallaghan/fbmysql-56/include/m_string.h:43,
                 from /home/mcallaghan/fbmysql-56/sql/debug_sync.h:35,
                 from /home/mcallaghan/fbmysql-56/storage/rocksdb/./rdb_iterator.h:22,
                 from /home/mcallaghan/fbmysql-56/storage/rocksdb/rdb_iterator.cc:17: