The top level source directory in a GCC distribution contains several files and directories that are shared with other software distributions such as that of GNU Binutils. It also contains several subdirectories that contain parts of GCC and its runtime libraries:
libiberty library.
libffi library, used as part of the Java runtime library.
libiberty library, used for portability and for some
generally useful data structures and algorithms. See Introduction (gnu libiberty), for more information
about this library.
libmudflap library, used for instrumenting pointer and array
dereferencing operations.
gccadmin account on gcc.gnu.org.
zlib compression library, used by the Java front end and as
part of the Java runtime library.
The build system in the top level directory, including how recursion into subdirectories works and how building runtime libraries for multilibs is handled, is documented in a separate manual, included with GNU Binutils. See GNU configure and build system (The GNU configure and build system), for details.