str: don't include alloca.h
str: don't include alloca.h

We shouldn't include alloca.h directly.  Instead, we should include
jeffpc/mem.h.

Signed-off-by: Josef 'Jeff' Sipek <a620f141433c70aa9e43778305a6c68cbfadfb25@josefsipek.net>

jeffpc/libjeffpc,jeffpc/libjeffpc,jeffpc/libjeffpc,jeffpc/libjeffpc