Portability fixes for Solaris Sun Studio and MacOS.

Only do -Wall by default if on GCC (or something that looks like
GCC, such as clang/llvm).

Turn on -Werror so we can get some better error-checking, but
we also need -Wno-deprecated-declarations at least for MacOS,
because daemon(3) is deprecated starting with MacOS 10.5.

Fixes #174 (I think).

Submitted by:	@marksolaris
Regen.