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
MFH: 2020Q2 (blanket: runtime fix)
Differential Revision: https://reviews.freebsd.org/D23246