Support building on macOS/arm64

On Arm-based Macs, -no_pie is ignored and gives a linker warning.
Moreover, the build falls over with:

  ld: Absolute addressing not allowed in arm64 code but used in '_image_type_ptr_aisimage' referencing '_image_type_aisimage'

for dumpimage and mkimage, since we put data structs in text sections
not data sections and so cannot have dynamic relocations. Instead, move
the sections to __DATA and drop disabling PIE.

Signed-off-by: Jessica Clarke <jrtc27@jrtc27.com>