Fix valgrind errors with MemMap::Sync().
This fixes valgrind-test-art-host-gtest-oat_test and one error in
Valgrind doesn't like it if an address range that contains noaccess or
uninitialized memory is passed to msync(). Temporarily lift the noaccess
protection of the lower-end redzone because msync accepts a page-aligned
base address only and exclude the higher-end noaccess redzone from the
1 file changed