configure: Refactor systemunitdir expression to use PKG_CHECK_VAR

Change-Id: Ia78044b47d2e01ec2629ba2bc7d8033c0107afb9
Signed-off-by: William A. Kennington III <wak@google.com>
diff --git a/bmc/firmware-handler/Makefile.am b/bmc/firmware-handler/Makefile.am
index f4d8e43..c12838d 100644
--- a/bmc/firmware-handler/Makefile.am
+++ b/bmc/firmware-handler/Makefile.am
@@ -25,7 +25,7 @@
 dist_pkgdata_DATA += config-bios.json
 endif
 
-if HAVE_SYSTEMD
+if HAVE_SYSTEMUNITDIR
 systemdsystemunit_DATA = \
 	phosphor-ipmi-flash-bmc-prepare.target \
 	phosphor-ipmi-flash-bmc-verify.target \
@@ -37,6 +37,7 @@
 	phosphor-ipmi-flash-bios-update.target
 endif
 endif
+
 # Convenience libraries that are discarded after build
 noinst_LTLIBRARIES = libfirmwareblob_common.la
 
diff --git a/configure.ac b/configure.ac
index 16d95e8..1532977 100644
--- a/configure.ac
+++ b/configure.ac
@@ -101,20 +101,17 @@
         [],
         [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="$def_systemdsystemunitdir"]
-         )]
-    )
-    AS_IF([test "x$with_systemdsystemunitdir" != "xno"],
-        [AC_SUBST([systemdsystemunitdir], [$with_systemdsystemunitdir])]
-    )
-    AM_CONDITIONAL([HAVE_SYSTEMD], [test "x$with_systemdsystemunitdir" != "xno"])
+    AS_IF([test "x$with_systemdsystemunitdir" = "xyes" -o "x$with_systemdsystemunitdir" = "xauto"], [
+        PKG_CHECK_VAR([SYSTEMUNITDIR], [systemd], [systemdsystemunitdir], [with_systemdsystemunitdir="$SYSTEMUNITDIR"], [])
+    ])
+    AS_IF([test "x$with_systemdsystemunitdir" = "xyes"], [
+        AC_MSG_ERROR([systemdsystemunitdir requested but pkg-config unable to query systemd package])
+    ])
+    AS_IF([test "x$with_systemdsystemunitdir" = "xno" -o "x$with_systemdsystemunitdir" = "xauto"], [
+        with_systemdsystemunitdir=''
+    ])
+    AC_SUBST([systemdsystemunitdir], ["$with_systemdsystemunitdir"])
+    AM_CONDITIONAL([HAVE_SYSTEMUNITDIR], [test "x$with_systemdsystemunitdir" != "x"])
 
     # Only set if build-bmc-blob-handler wasn't unset.
     AM_CONDITIONAL([ENABLE_HOST_BIOS], [test "x$enable_host_bios" = "xyes"])
@@ -122,7 +119,6 @@
         AX_APPEND_COMPILE_FLAGS([-DENABLE_HOST_BIOS], [CXXFLAGS])
     ])
 ], [
-    AM_CONDITIONAL([HAVE_SYSTEMD], [0])
     AM_CONDITIONAL([ENABLE_HOST_BIOS], [0])
 ])