Add support out-of-tree builds.
This commit adds a support for out-of-tree builds, i.e, object files,
executables and so on are writen to `$(OUTDIR)` (which defaults to
`build/<BUILD_TARGET>` directory.
This allows building Smalltalk/X from single source tree for multiple
targets.
#!stx --script
"/
"/ on any system:
"/ "stx --script script1.stx
"/ or:
"/ "stx --f script.stx"
"/ or:
"/ "stx script1.stx"
"/
"/ on Unix:
"/ make this file executable,
"/ ensure that stx is in your path,
"/ then type ./script1.stx
"/
"/ will just print some numbers
"/
1 to:10 do:[:i |
('the factorial of %1 is %2'
bindWith:i with:i factorial) printCR
].