Detecting Autoconf and Including Additional M4 Files

[Christopher Key]

Hello,

I'm completely new to autotools and am trying to autoconfiscate a pretty 
simple existing package, and I've a couple of questions.

Firstly, some sections of the code are endian dependent.  Autoconf has a 
test, AC_C_BIGENDIAN, which defines WORDS_BIGENDIAN on big endian 
systems, does nothing on little endian systems, and issues an error if 
endianness couldn't be detected.  This is fine when you know that 
autoconf has definately been used; the absence of WORDS_BIGENDIAN 
specifically implies a little endian system.  However, clearly this is 
not the case if the code is being compiled entirely separately from 
autoconf, e.g. in MSVC.  Hence, what I'd like to do is to be able to 
detect whether autoconf has been used, and act appropriately, e.g.

#ifdef USED_AUTOCONF
#ifdef WORDS_BIGENDIAN
do stuff for big endian systems
#else
do stuff for little endian systems
#endif
#else
#ifndef BYTE_ORDER
#error Please set BYTE_ORDER
#elseif BYTE_ORDER == BIG_ENDIAN
do stuff for big endian systems
#elseif BYTE_ORDER == LITTLE_ENDIAN
do stuff for little endian systems
#else
#error Unknown BYTE_ORDER
#endif
#endif

Bascially, what I'm wondering is whether this is the best way to do 
this, whether there's any standard name for 'USED_AUTOCONF', and where 
the best place to set it is.


Secondly, I'm also wanting to detect whether there an arithmetic right 
shift available.  I've found a test that does this, and have put it in 
package/m4/asr.m4.  What I'm wondering is how to ensure that this file 
is included.  The only way I've found to achieve this is to add 
'ACLOCAL_AMFLAGS = -I m4' to package/Makefile.am, but this doesn't seem 
quite right.  I've seen adding 'AC_SUBST(ACLOCAL_AMFLAGS, "-I m4")' to 
configure.ac suggested online, but this didn;t seem to do the trick.  
Any suggestions?

Regards,

Chris