How to specify srcdir?

[Matej Tyc]

I have the following project directory structure:
The root, where configure.ac is located
/src, where the source code resides
/lib, where the library is built
/bin, where the frontend is built.
Each of those directories have their own Makefile.am
I have learned that I should use this construction in those Makefiles.am:
srcdir = @srcdir@ and that I should use the AC_CONFIG_SRCDIR