graphics/jpeg-turbo: Apply upstream patch to fix riscv64

Architectures like riscv64 where WITH_SIMD takes its default value of 1
but the SIMD detection finds no support (due to, in the case of 3.1.4.1
for riscv64, there being no RVV support at all) were broken as they
would still try to build simdcoverage and fail to link it. Apply the
upstream fix from the 3.1.x branch.

PR: 296754
Reviewed by: desktop (arrowd)
Approved by: desktop (arrowd)
MFH: 2026Q3

(cherry picked from commit 23ed1126e58b9858f36e5e4d58c077197643dcab)