config.mk: improve feature test macros and compatibility

- add missing header netinet/in.h for socket declarations (POSIX).
- rename sendfile to responsefile, sendfile(2) is a syscall on FreeBSD.
- remove _XOPEN_SOURCE: this will give a warning about strptime on Linux
  glibc, but unbreaks the build on NetBSD and FreeBSD.

thanks also to josuah and quinq for testing!

config.mk

@@ -8,7 +8,7 @@ PREFIX = /usr/local
 MANPREFIX = $(PREFIX)/share/man
 
 # flags
-CPPFLAGS = -DVERSION=\"$(VERSION)\" -D_DEFAULT_SOURCE -D_XOPEN_SOURCE=700 -D_BSD_SOURCE
+CPPFLAGS = -DVERSION=\"$(VERSION)\" -D_DEFAULT_SOURCE -D_BSD_SOURCE
 CFLAGS   = -std=c99 -pedantic -Wall -Os
 LDFLAGS  = -s
 

quark.c

@@ -1,4 +1,5 @@
 /* See LICENSE file for license details. */
+#include <netinet/in.h>
 #include <sys/resource.h>
 #include <sys/socket.h>
 #include <sys/stat.h>
@@ -418,7 +419,7 @@ cleanup:
 }
 
 static enum status
-sendfile(int fd, char *name, struct request *r, struct stat *st, char *mime,
+responsefile(int fd, char *name, struct request *r, struct stat *st, char *mime,
          off_t lower, off_t upper)
 {
 	FILE *fp;
@@ -754,7 +755,7 @@ sendresponse(int fd, struct request *r)
 		}
 	}
 
-	return sendfile(fd, RELPATH(realtarget), r, &st, mime, lower, upper);
+	return responsefile(fd, RELPATH(realtarget), r, &st, mime, lower, upper);
 }
 
 static void