Basic CMake system

To create an Eclipse project that should be equivalent to the old one

   cmake -G "Eclipse CDT4 - Unix Makefiles" .

To generate the default (just a Makefile)

   cmake .

This commit also adds a helper "configure" script so that `./configure && make` does the right thing.

I wasn't able to build the syscall wrapper library with this system.  I see

    /home/cjones/rr/rr/src/share/wrap_syscalls.c: In function ‘clock_gettime’:
    /home/cjones/rr/rr/src/share/wrap_syscalls.c:290:2: error: inconsistent operand constraints in an ‘asm’

I'm not sure if this was already broken and disabled, or these commits broke something.  Checking on that now.