Move simple_httpd out of picobsd, add HTTPD option (default OFF)

picobsd/tinyware has had this compact HTTPD server for a long time, and some
people do use it. Move it out into usr.sbin well in advance of any action
being taken on picobsd.

This has been gated behind an HTTPD option defaulted to *off*, primarily for
two reasons:
1.) This code likely needs a good audit, as it's been living off in picobsd
    land for a long time, and
2.) We don't currently ship an httpd and this may not be a welcome surprise.

Reviewed by:	eugen
Differential Revision:	https://reviews.freebsd.org/D21724

share/mk/src.opts.mk

@@ -198,6 +198,7 @@ __DEFAULT_NO_OPTIONS = \
     EXPERIMENTAL \
     GNU_GREP_COMPAT \
     HESIOD \
+    HTTPD \
     LIBSOFT \
     LOADER_FIREWIRE \
     LOADER_FORCE_LE \

tools/build/options/WITHOUT_HTTPD

@@ -0,0 +1,2 @@
+.\" $FreeBSD$
+Set to neither build nor install httpd

tools/build/options/WITH_HTTPD

@@ -0,0 +1,2 @@
+.\" $FreeBSD$
+Set to build and install httpd

usr.sbin/Makefile

@@ -138,6 +138,7 @@ SUBDIR.${MK_FMTREE}+=	fmtree
 SUBDIR.${MK_FREEBSD_UPDATE}+=	freebsd-update
 SUBDIR.${MK_GSSAPI}+=	gssd
 SUBDIR.${MK_GPIO}+=	gpioctl
+SUBDIR.${MK_HTTPD}+=	httpd
 SUBDIR.${MK_INET6}+=	ip6addrctl
 SUBDIR.${MK_INET6}+=	mld6query
 SUBDIR.${MK_INET6}+=	ndp

usr.sbin/httpd/Makefile

@@ -1,7 +1,7 @@
 # $FreeBSD$
 #
-PROG=simple_httpd
+PROG=	httpd
-SRCS= 	simple_httpd.c
+SRCS=	simple_httpd.c
 MAN=
 WARNS?=6