0.7.0 build failure on AArch64

[rbtcollins]

You can see the failed run here https://github.com/rbtcollins/effective-limits.rs/pull/9/checks?check_run_id=820016011:

(and the github action config there might be useful, if you want CI coverage of more platforms)

   Compiling sys-info v0.7.0
error[E0308]: mismatched types
   --> /cargo/registry/src/github.com-1ecc6299db9ec823/sys-info-0.7.0/lib.rs:618:22
    |
618 | pub fn boottime() -> Result<timeval, Error> {
    |        --------      ^^^^^^^^^^^^^^^^^^^^^^ expected enum `std::result::Result`, found `()`
    |        |
    |        implicitly returns `()` as its body has no tail or `return` expression
    |
    = note:   expected enum `std::result::Result<libc::timeval, Error>`
            found unit type `()`

error: aborting due to previous error

For more information about this error, try `rustc --explain E0308`.
The following warnings were emitted during compilation:

warning: c/linux.c:42:9: warning: implicit declaration of function 'get_nprocs' is invalid in C99 [-Wimplicit-function-declaration]
warning:         return get_nprocs();
warning:                ^
warning: c/linux.c:96:11: warning: implicitly declaring library function 'index' with type 'char *(const char *, int)' [-Wimplicit-function-declaration]
warning:                 mount = index(procline, ' ');
warning:                         ^
warning: c/linux.c:96:11: note: include the header <strings.h> or explicitly provide a declaration for 'index'

[rbtcollins]

Thank you for fixing this, but it would be really lovely and much more useful to also get a release ;).