[PATCH v4l-utils v2 1/2] configure.ac: autodetect availability of systemd

["Ulrich Ölmann" <u.oelmann@pengutronix.de>]

Import systemd's official suggestion [1] how this should be handled in packages
using autoconf. A side effect of this is the removal of the hardcoded fallback
path "/lib/systemd/system" which leaks build host information when cross
compiling v4l-utils and therefore defeats reproducible builds.

[1] https://www.freedesktop.org/software/systemd/man/daemon.html#Installing%20systemd%20Service%20Files

Signed-off-by: Ulrich Ölmann <u.oelmann@pengutronix.de>
---
v1 --> v2:
  - fixed autodetection
  - extended commit message

 configure.ac | 10 +++++++++-
 1 file changed, 9 insertions(+), 1 deletion(-)

diff --git a/configure.ac b/configure.ac
index 727730c5ccf4..8470116df4b1 100644
--- a/configure.ac
+++ b/configure.ac
@@ -388,7 +388,15 @@ AC_ARG_WITH(udevdir,
 AC_ARG_WITH(systemdsystemunitdir,
 	AS_HELP_STRING([--with-systemdsystemunitdir=DIR], [set systemd system unit directory]),
 	[],
-	[with_systemdsystemunitdir=`$PKG_CONFIG --variable=systemdsystemunitdir systemd || echo /lib/systemd/system`])
+	[with_systemdsystemunitdir=auto])
+AS_IF([test "x$with_systemdsystemunitdir" = "xyes" -o "x$with_systemdsystemunitdir" = "xauto"],
+      [def_systemdsystemunitdir=$($PKG_CONFIG --variable=systemdsystemunitdir systemd)
+       AS_IF([test "x$def_systemdsystemunitdir" = "x"],
+             [AS_IF([test "x$with_systemdsystemunitdir" = "xyes"],
+                    [AC_MSG_ERROR([systemd support requested but pkg-config unable to query systemd package])])
+              with_systemdsystemunitdir=no],
+             [with_systemdsystemunitdir="$def_systemdsystemunitdir"])])
+AM_CONDITIONAL([HAVE_SYSTEMD], [test "x$with_systemdsystemunitdir" != "xno"])
 
 # Generic check: works with most distributions
 def_gconv_dir=`for i in /lib64 /usr/lib64 /usr/local/lib64 /lib /usr/lib /usr/local/lib; do if @<:@ -d \$i/gconv @:>@; then echo \$i/gconv; break; fi; done`
-- 
2.29.2