* fix libc prototypes of offsets to have correct integer sizes and
   signedness. This gets all behavior tests to pass for
   armv8-linux-musleabihf
 * fix linux mmap syscall to have correct integer size and signedness
   for offset
 * disable failing armv8-linux-musleabihf std lib tests. See 3289. I
   suspect compiler-rt issue. Note these tests fail with this target
   triple regardless of whether musl is actually linked (-lc).