Setting thread names using prctl syscall

[Habush]

Setting thread names using prctl syscall results in the atomspace only building on Linux as the syscall is specific to Linux. This was added in #2832.

[linas]

I assume you are building on Apple; to stub it out, you just need to add something like

#ifdef MACOS
#define prctl(a,b,c,d,e) {}
#endif

to cogutils/opencog/util/platform.h and then make sure platform.h is included where needed. ... If there's an equivalent call on apple, then it can be added to platform.cc (which, after reading, looks like its old messy and needs a major cleanup.) That's probably the best solution.