net/rsync-bpc: fix build on armv7

Supply GNU_CONFIGURE=yes instead of HAS_CONFIGURE=yes so that the right
magic is passed to work around the error

checking build system type... Invalid configuration armv7-unknown-freebsd15.1-gnueabihf': machine armv7-unknown-freebsd15.1' not recognized

Approved by: portmgr (build fix blanket)
MFH: 2026Q3

(cherry picked from commit 977fa78a30b4c9045da3dc080d11de9feb0dc3b9)