path\to\Eclipse Java workspace\SweetHome3D>ant
Buildfile: path\to\Eclipse Java workspace\SweetHome3D\build.xml
build:
[javac] path\to\Eclipse Java workspace\SweetHome3D\build.xml:45: warning: 'includeantruntime' was not set, defaulting to build.sysclasspath=last; set to false for repeatable builds
[javac] Compiling 2 source files to path\to\Eclipse Java workspace\SweetHome3D\build\classes
[javac] warning: [options] bootstrap class path not set in conjunction with -source 1.3
[javac] error: Source option 1.3 is no longer supported. Use 1.6 or later.
[javac] error: Target option 1.1 is no longer supported. Use 1.6 or later.
BUILD FAILED
You'll have to compile with JDK 8, because JDK 9 removed support for [font=courier new]-source[/font] and [font=courier new]-target[/font] javac options with a value less than 1.6.