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

(cherry picked from commit 8de51b589fa0daa00ebfee7a4ec8ee91bc968f7b)
Signed-off-by: Bruce A. Mah <bmah@es.net>

Conflicts:
	configure.ac
Another try at portability.  Don't do -Werror.  While probably
the best thing to do from a code hygeine standpoint, it's too
painful to try to get right for now.

Fixes #174 (second try).

(cherry picked from commit 94c0bfffcb9b79370af3e445a813131359a806e4)
Signed-off-by: Bruce A. Mah <bmah@es.net>

Conflicts:
	configure.ac
Regen.