Revert "build: use literals for AC_CHECK_HEADERS/AC_CHECK_FUNCS"

That commit was wrong, it breaks syntax for autoconf <2.71, since
AC_CHECK_*S() requires sh-like list.

This reverts commit 28f0fe6fd1e2b1e9fb24a5c7a5b078790890e44f.

Fixes: #1149

configure.ac

@@ -185,40 +185,40 @@ LIBEVENT_OPENSSL
 LIBEVENT_MBEDTLS
 
 dnl Checks for header files.
-AC_CHECK_HEADERS([
-  arpa/inet.h
-  fcntl.h
-  ifaddrs.h
-  mach/mach_time.h
-  mach/mach.h
-  netdb.h
-  netinet/in.h
-  netinet/in6.h
-  netinet/tcp.h
-  sys/un.h
-  poll.h
-  port.h
-  stdarg.h
-  stddef.h
-  sys/devpoll.h
-  sys/epoll.h
-  sys/event.h
-  sys/eventfd.h
-  sys/ioctl.h
-  sys/mman.h
-  sys/param.h
-  sys/queue.h
-  sys/resource.h
-  sys/select.h
-  sys/sendfile.h
-  sys/socket.h
-  sys/stat.h
-  sys/time.h
-  sys/timerfd.h
-  sys/uio.h
-  sys/wait.h
-  sys/random.h
-  errno.h
+AC_CHECK_HEADERS([ \
+  arpa/inet.h \
+  fcntl.h \
+  ifaddrs.h \
+  mach/mach_time.h \
+  mach/mach.h \
+  netdb.h \
+  netinet/in.h \
+  netinet/in6.h \
+  netinet/tcp.h \
+  sys/un.h \
+  poll.h \
+  port.h \
+  stdarg.h \
+  stddef.h \
+  sys/devpoll.h \
+  sys/epoll.h \
+  sys/event.h \
+  sys/eventfd.h \
+  sys/ioctl.h \
+  sys/mman.h \
+  sys/param.h \
+  sys/queue.h \
+  sys/resource.h \
+  sys/select.h \
+  sys/sendfile.h \
+  sys/socket.h \
+  sys/stat.h \
+  sys/time.h \
+  sys/timerfd.h \
+  sys/uio.h \
+  sys/wait.h \
+  sys/random.h \
+  errno.h \
   afunix.h
 ])
 
@@ -325,40 +325,40 @@ AC_C_INLINE
 AC_HEADER_TIME
 
 dnl Checks for library functions.
-AC_CHECK_FUNCS([
-  accept4
-  arc4random
-  arc4random_buf
-  arc4random_addrandom
-  eventfd
-  epoll_create1
-  fcntl
-  getegid
-  geteuid
-  getifaddrs
-  gettimeofday
-  issetugid
-  mach_absolute_time
-  mmap
-  nanosleep
-  pipe
-  pipe2
-  putenv
-  sendfile
-  setenv
-  setrlimit
-  sigaction
-  signal
-  strsignal
-  strlcpy
-  strsep
-  strtok_r
-  strtoll
-  sysctl
-  timerfd_create
-  umask
-  unsetenv
-  usleep
+AC_CHECK_FUNCS([ \
+  accept4 \
+  arc4random \
+  arc4random_buf \
+  arc4random_addrandom \
+  eventfd \
+  epoll_create1 \
+  fcntl \
+  getegid \
+  geteuid \
+  getifaddrs \
+  gettimeofday \
+  issetugid \
+  mach_absolute_time \
+  mmap \
+  nanosleep \
+  pipe \
+  pipe2 \
+  putenv \
+  sendfile \
+  setenv \
+  setrlimit \
+  sigaction \
+  signal \
+  strsignal \
+  strlcpy \
+  strsep \
+  strtok_r \
+  strtoll \
+  sysctl \
+  timerfd_create \
+  umask \
+  unsetenv \
+  usleep \
   getrandom
 ])