Specify the programming language in which a source file is written.
A property that can be set to indicate what programming language the
source file is. If it is not set the language is determined based on
the file extension. Typical values are
CXX (i.e. C++),
this property for a file means this file will be compiled, unless
HEADER_FILE_ONLY is set.
Changed in version 3.20: Setting this property causes the source file to be compiled as the
specified language, using explicit flags if possible. Previously it
only caused the specified language's compiler to be used.