#24 Fix build with clang 15+

[Khem Raj]

compiling expect with clang15 results in bunch of errors which use to be warning thus far but now compilers are getting stricter

| ../../../../../../../workspace/sources/expect/exp_clib.c:2875:2: error: call to undeclared function 'setsid'; ISO C99 and later do not support implicit function declarations [-Wimplicit-function-declaration]

Attached patch fixes such cases.

[Florian Weimer]

Additional changes are required in the configure script. I'm attaching what we will be using in Fedora.

[Florian Weimer]

And another fix for exp_chan.c. This ports expect to the current channel code (I hope).