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 used in the vanilla
luaJIT source after e496a502b0686af25053c161752c044074edc44e

The same issue had been reported in Torch7-distro (https://github.com/torch/torch7-distro/issues/134) and it also can be fixed with this commit without touching any file location.