Fix libsystemd detection

1. Use uppercase for `prefix` parameter
   `SYSTEMD_CFLAGS` is used elsewhere so `prefix` cannot be lowercase.
   https://autotools.info/pkgconfig/pkg_check_modules.html

2. The module name should be `libsystemd`
   Previously it will result in the following compile error when building pppd/auth.c:
   > /usr/bin/ld: pppd-auth.o: undefined reference to symbol 'sd_notify@@LIBSYSTEMD_209'
   > /usr/bin/ld: /usr/lib/libsystemd.so.0: error adding symbols: DSO missing from command line

   This is due to missing `-lsystemd-daemon` flag which is provided by `libsystemd-daemon-devel`
   package on Debian or `systemd-libs` on ArchLinux. And the proper .pc file in the package is
   `libsystemd` not `systemd`.
   https://stackoverflow.com/a/38303241

Signed-off-by: Chocobo1 <Chocobo1@users.noreply.github.com>

diff --git a/configure.ac b/configure.ac
index 7b4c84295cf086c081b54ada7062c6347b6672f2..184213e09607d79de4781bae9c3b6f127863ac29 100644 (file)
--- a/configure.ac
+++ b/configure.ac
@@ -106,7 +106,7 @@ AM_CONDITIONAL(WITH_SYSTEMD, test "x${enable_systemd}" = "xyes")
 AM_COND_IF([WITH_SYSTEMD],
     AC_DEFINE([SYSTEMD], 1, [Enable support for systemd notifications]))
 AS_IF([test "x${enable_systemd}" = "xyes"], [
-       PKG_CHECK_MODULES([systemd], [systemd])])
+       PKG_CHECK_MODULES([SYSTEMD], [libsystemd])])
 
 #
 # Enable Callback Protocol Support, disabled by default