Add a few more error checks and adjustments to reglap.

Add a few more error checks and adjustments to reglap.

In util/ncgg, add two more errors for tables using reglap:
 - "Two sizes of reg_float can't be same size"
 - "Missing reg_float of size %d to contain %s"

In mach/proto/ncg, rename macro isregvar_size() to PICK_REGVAR(), so
the macro doesn't look like a function.  This macro sometimes doesn't
evaluate its second argument.

In mach/powerpc/ncg/mach.c, change type of lfs_set to uint32_t, and
change the left shifts from 1U<<regno to (uint32_t)1<<regno, because
1U would be too small for machines with 16-bit int.