[librsvg: 1/9] configure: Simplify setting defaults for empty vars

[Marge Bot <marge-bot src gnome org>]

commit 74a2568a6b47d8ee167463627931f4094aa5446d
Author: Ismael Luceno <ismael iodev co uk>
Date:   Sat Sep 11 17:44:34 2021 +0200

    configure: Simplify setting defaults for empty vars
    
    Substitution can be used to set a default value for empty/unset variables.
    
    Part-of: <https://gitlab.gnome.org/GNOME/librsvg/-/merge_requests/586>

 configure.ac | 8 ++------
 1 file changed, 2 insertions(+), 6 deletions(-)
---
diff --git a/configure.ac b/configure.ac
index 6e442d5f..5feaafe8 100644
--- a/configure.ac
+++ b/configure.ac
@@ -255,9 +255,7 @@ fi
 AM_CONDITIONAL([DEBUG_RELEASE], [test "x$debug_release" = "xyes"])
 
 AC_ARG_VAR(RUST_TARGET, [Set rust target (default=$host)])
-if test "x$RUST_TARGET" = x; then
-       RUST_TARGET=$host
-fi
+: ${RUST_TARGET:=$host}
 
 AM_CONDITIONAL(CROSS_COMPILING, test $cross_compiling = yes)
 if test "x$cross_compiling" = "xyes" ; then
@@ -269,9 +267,7 @@ dnl ===========================================================================
 dnl Build introspectable bindings
 
 # No automagic please!
-if test -z "$enable_introspection"; then
-  enable_introspection=yes
-fi
+: ${enable_introspection:=yes}
 
 GOBJECT_INTROSPECTION_CHECK([0.10.8])