devel/volk: Fix build on armv7.

This port does not build on armv7 due to inline assembly unsupported by clang.
Fix the build by compiling with gcc on armv7.

PR: 259447
Approved by: portmgr (build fix blanket)

(cherry picked from commit 79ede500f770ed197458e9ae7cf87b2961c4dc16)