On x86 archs (both 32 and 64 bit) a bool return value only sets the 8-bit
al register, and the higher bits of the ax register have an undefined
value.  When testing the return value of such cases it is required to just
test al for zero/non-zero.  On the other hand, checking for truth or
zero/non-zero on an integer return value requires checking all bits of the
register.  These two cases must be distinguished and handled correctly in
generated native code.  This patch makes sure of this.

For other supported native archs (ARM, Thumb2, Xtensa) there is no such
distinction and this patch does not change anything for them.

All the asm macro names that convert a particular architecture to a generic
interface now follow the convention whereby the "destination" (usually a
register) is specified first.

For archs that have 16-bit pointers, the asmxtensa.h file can give compiler
warnings about left-shift being greater than the width of the type (due to
the inline functions in this header file).  Explicitly casting the
constants to uint32_t stops these warnings.