emulators/qemu40: Apply upstream fix for cacheline detection on big endian

Backport qemu 5ca156cfde0f3821f15988619e51cf3cda99aaa6, which fixes 
cacheline detection on big-endian to use the correct sized variable to 
store the sysctl result.

Fixes "Assertion failed: ((isize & (isize - 1)) == 0)" on BE platforms. 

Reviewed by:    bofh, pkubaj
Approved by:    pkubaj
Obtained from:  qemu
Differential Revision:  https://reviews.freebsd.org/D23246