Distcheck and multiple development builds

[Hans Åberg]

As 'make distcheck' puts the sources in a readonly directory, the bison output 
sources must be copied to the compilation directory. However, when developing 
using multiple out-of-source builds, necessary to avoid compiler confusion, I 
want the bison compilation to be in the source tree, so that the compiled 
sources comes along with the distribution. What is the recommended way to 
achieve that?