configure: pull AR from the env too

This matches the existing CC behavior.

Signed-off-by: Mike Frysinger <vapier@gentoo.org>
diff --git a/configure b/configure
index ea1038d..7c2db9b 100755
--- a/configure
+++ b/configure
@@ -10,7 +10,9 @@
 check_toolchain()
 {
 : ${PKG_CONFIG:=pkg-config}
+: ${AR=ar}
 : ${CC=gcc}
+echo "AR:=${AR}" >>Config
 echo "CC:=${CC}" >>Config
 echo "PKG_CONFIG:=${PKG_CONFIG}" >>Config
 }