Specifiy both source ant target Java versions
...when compiling Java code. Since `stx:libjava` only supports Java 7,
make sure all code is compiled targeting Java 7.
LIBRARY libjava
DESCRIPTION 'AddOn library for ST/X'
CODE EXECUTE READ SHARED
DATA READ WRITE
SECTIONS
INITCODE READ EXECUTE SHARED
INITDATA READ WRITE
EXPORTS
_libjava_Init