6.3.8.2 The Front End config-lang.in File
Each language subdirectory contains a config-lang.in file.
This file is a shell script that may define some variables describing
the language:
language- This definition must be present, and gives the name of the language
for some purposes such as arguments to --enable-languages.
lang_requires- If defined, this variable lists (space-separated) language front ends
other than C that this front end requires to be enabled (with the
names given being their
language settings). For example, the
Java front end depends on the C++ front end, so sets
‘lang_requires=c++’.
subdir_requires- If defined, this variable lists (space-separated) front end directories
other than C that this front end requires to be present. For example,
the Objective-C++ front end uses source files from the C++ and
Objective-C front ends, so sets ‘subdir_requires="cp objc"’.
target_libs- If defined, this variable lists (space-separated) targets in the top
level Makefile to build the runtime libraries for this
language, such as
target-libobjc.
lang_dirs- If defined, this variable lists (space-separated) top level
directories (parallel to gcc), apart from the runtime libraries,
that should not be configured if this front end is not built.
build_by_default- If defined to ‘no’, this language front end is not built unless
enabled in a --enable-languages argument. Otherwise, front
ends are built by default, subject to any special logic in
configure.ac (as is present to disable the Ada front end if the
Ada compiler is not already installed).
boot_language- If defined to ‘yes’, this front end is built in stage1 of the
bootstrap. This is only relevant to front ends written in their own
languages.
compilers- If defined, a space-separated list of compiler executables that will
be run by the driver. The names here will each end
with ‘\$(exeext)’.
outputs- If defined, a space-separated list of files that should be generated
by configure substituting values in them. This mechanism can
be used to create a file language/Makefile from
language/Makefile.in, but this is deprecated, building
everything from the single gcc/Makefile is preferred.
gtfiles- If defined, a space-separated list of files that should be scanned by
gengtype.c to generate the garbage collection tables and routines for
this language. This excludes the files that are common to all front
ends. See Type Information.