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.
OperatingSystem isUNIXlike ifTrue:[
| fontNormal fontMonospace |
fontNormal := XftFontDescription family: 'Sans' size: 10.
fontMonospace := XftFontDescription family: 'Monospace' size: 10.
SimpleView defaultFont: fontNormal.
CheckLabel defaultFont: fontNormal.
CheckBox defaultFont: fontNormal.
CheckLabel defaultFont: fontNormal.
Button defaultFont: fontNormal.
Toggle defaultFont: fontNormal.
SelectionInListView defaultFont: fontNormal.
MenuView defaultFont: fontNormal.
MenuPanel defaultFont: fontNormal.
NoteBookView defaultFont: fontNormal.
PullDownMenu defaultFont: fontNormal.
TextView defaultFont: fontNormal.
EditTextView defaultFont: fontNormal.
CodeView defaultFont: fontMonospace.
]