Add tcl private headers to CFLAGS 

compiling expect fails trying to find the tcl private headers:

    expect.c:28:10: fatal error: 'tclInt.h' file not found
    #include "tclInt.h"
             ^
    exp_command.c:61:10: fatal error: 'tclInt.h' file not found
    #include "tclInt.h"             /* need OpenFile */
             ^
    1 error generated.
    make: *** [expect.o] Error 1
    make: *** Waiting for unfinished jobs....
    1 error generated.
    make: *** [exp_command.o] Error 1

I added the tcl private headers directory to the CPATH and now expect compiles successfully:

    system "make","CFLAGS=-I/System/Library/Frameworks/Tcl.framework/Versions/Current/Headers/tcl-private"