[PATCH 6/7] build-sys: use backticks rather than $() for commands in configure

[Sami Kerola <kerolasa@iki.fi>]

The configure had both backticks and $() in use.  These command
susbstitutions are mutually interchangeable, so one should pick only one
form.  In this case backticks were favored because they are known with
greater range of shells, making the backticks to be more portable.

References: https://www.gnu.org/software/autoconf/manual/autoconf-2.67/html_node/Shell-Substitutions.html#index-g_t_0024_0028_0040var_007bcommands_007d_0029-1632
Signed-off-by: Sami Kerola <kerolasa@iki.fi>
---
 configure.ac | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/configure.ac b/configure.ac
index 6fae31e..7252e9b 100644
--- a/configure.ac
+++ b/configure.ac
@@ -1347,7 +1347,7 @@ AS_IF([test "x$enable_socket_activation" = xyes], [
 
 AC_ARG_WITH([systemdsystemunitdir],
   AS_HELP_STRING([--with-systemdsystemunitdir=DIR], [directory for systemd service files]),
-  [], [with_systemdsystemunitdir=$($PKG_CONFIG --variable=systemdsystemunitdir systemd)])
+  [], [with_systemdsystemunitdir=`$PKG_CONFIG --variable=systemdsystemunitdir systemd`])
 
 AS_IF([test "x$with_systemdsystemunitdir" != "xno"], [
   AC_SUBST([systemdsystemunitdir], [$with_systemdsystemunitdir])
@@ -1359,8 +1359,8 @@ AM_CONDITIONAL([HAVE_SYSTEMD], [test -n "$with_systemdsystemunitdir" -a "x$with_
 AC_ARG_WITH([bashcompletiondir],
   AS_HELP_STRING([--with-bashcompletiondir=DIR], [Bash completions directory]),
   [],
-  [AS_IF([$($PKG_CONFIG --exists bash-completion)], [
-    with_bashcompletiondir=$($PKG_CONFIG --variable=completionsdir bash-completion)
+  [AS_IF([`$PKG_CONFIG --exists bash-completion`], [
+    with_bashcompletiondir=`$PKG_CONFIG --variable=completionsdir bash-completion`
   ], [
     with_bashcompletiondir=${datadir}/bash-completion/completions
   ])
-- 
1.8.3.4