HASFPU flag to DynASM fails to build on ARM

buildvm_arch.h generated with HASFPU flag does not work on ARM. Using
FPU flag resolves this problem. The same flag is also found in the
luaJIT source after e496a502b0686af25053c161752c044074edc44e
Merge pull request #2 from jhjin/master

HASFPU flag to DynASM fails to build on ARM