[Ltib] boost-1.31.0 fails to build

[Robert P. J. Day]

  i'm prepared to believe that i've just done something silly here,  
but i added boost-1.31.0 to my ltib build and got a build error that i  
(sort of) know the cause of.

  after adding boost, i get:

... snip ...
###
### Using 'gcc' toolset.
###
rm -rf bootstrap.gcc
mkdir bootstrap.gcc
gcc -o bootstrap.gcc/jam0 command.c compile.c execnt.c execunix.c  
execvms.c expand.c filent.c fileos2.c fileunix.c filevms.c glob.c  
hash.c hdrmacro.c headers.c jam.c jambase.c jamgram.c lists.c make.c  
make1.c newstr.c option.c parse.c pathunix.c pathvms.c regexp.c  
rules.c scan.c search.c subst.c timestamp.c variable.c modules.c  
strings.c filesys.c builtins.c pwd.c class.c native.c modules/set.c  
modules/path.c modules/regex.c modules/property-set.c modules/sequence.c
execunix.c: In function 'execcmd':
execunix.c:228: warning: incompatible implicit declaration of built-in  
function '_exit'
./bootstrap.gcc/jam0 -f build.jam --toolset=gcc --toolset-root= clean
./build.sh: line 16: ./bootstrap.gcc/jam0: cannot execute binary file
++ find tools/build/jam_src/ -name bjam -a -type f
+ BJAM=
... snip ...

  it's that "./bootstrap.gcc/jam0: cannot execute binary file" that  
appears to be the problem, and that's because, while that file exists,  
it's a cross-compiled executable:

$ file jam0
jam0: ELF 32-bit MSB executable, Motorola version 1 (SYSV), for  
GNU/Linux 2.6.10, dynamically linked (uses shared libs), not stripped

  if you look at the boost.spec file, it certainly appears that you  
need to run jam as the last step in the packaging process on the build  
system, so having a cross-compiled version of "jam" is obviously not  
going to help -- it needs to be a native (x86) version.

  or have i done something dumb?

rday