configure: Detect AIX ar command instead of hardcoding it in the OS section

configure

@@ -2707,6 +2707,9 @@ if $ar 2>&1 | grep -q Microsoft; then
 elif $ar 2>&1 | grep -q 'Texas Instruments'; then
     arflags="rq"
     ar_o='$@'
+elif $ar 2>&1 | grep -q 'Usage: ar.*-X.*any'; then
+    arflags='-Xany -r -c'
+    ar_o='$@'
 else
     arflags="rc"
     ar_o='$@'
@@ -3053,7 +3056,6 @@ case $target_os in
         SHFLAGS=-shared
         add_cppflags '-I\$(SRC_PATH)/compat/aix'
         enabled shared && add_ldflags -Wl,-brtl
-        ar_default='ar -Xany'
         ;;
     haiku)
         prefix_default="/boot/common"