See bug #67635

Improve previous fix:
- also rely on pkg-config for systemd < 209
- always check for header
- comments

Author: remicollet

sapi/fpm/config.m4

@@ -572,17 +572,29 @@ if test "$PHP_FPM" != "no"; then
     fi
     unset SYSTEMD_LIBS
     unset SYSTEMD_INCS
+
     if test -x "$PKG_CONFIG" && $PKG_CONFIG --exists libsystemd; then
+      dnl systemd version >= 209 provides libsystemd
       AC_MSG_CHECKING([for libsystemd])
       SYSTEMD_LIBS=`$PKG_CONFIG --libs libsystemd`
       SYSTEMD_INCS=`$PKG_CONFIG --cflags-only-I libsystemd`
       SYSTEMD_VERS=`$PKG_CONFIG --modversion libsystemd`
-      HAVE_SD_DAEMON_H="yes"
       AC_MSG_RESULT([version $SYSTEMD_VERS])
+
+    elif test -x "$PKG_CONFIG" && $PKG_CONFIG --exists libsystemd-daemon; then
+      dnl systemd version < 209 provides libsystemd-daemon
+      AC_MSG_CHECKING([for libsystemd-daemon])
+      SYSTEMD_LIBS=`$PKG_CONFIG --libs libsystemd-daemon`
+      SYSTEMD_INCS=`$PKG_CONFIG --cflags-only-I libsystemd-daemon`
+      SYSTEMD_VERS=`$PKG_CONFIG --modversion libsystemd-daemon`
+      AC_MSG_RESULT([version $SYSTEMD_VERS])
+
     else
+      dnl failback when no pkg-config
       AC_CHECK_LIB(systemd-daemon, sd_notify, SYSTEMD_LIBS="-lsystemd-daemon")
-      AC_CHECK_HEADERS(systemd/sd-daemon.h, [HAVE_SD_DAEMON_H="yes"], [HAVE_SD_DAEMON_H="no"])
     fi
+
+    AC_CHECK_HEADERS(systemd/sd-daemon.h, [HAVE_SD_DAEMON_H="yes"], [HAVE_SD_DAEMON_H="no"])
     if test $HAVE_SD_DAEMON_H = "no" || test -z "${SYSTEMD_LIBS}"; then
       AC_MSG_ERROR([Your system does not support systemd.])
     else