libtool.m4: Fix missing quotes for lt_ar_flags

lt_ar_flags are unquoted, which causes failures when additional options
are passed to ARFLAGS.

Reported: https://savannah.gnu.org/support/?111257

* m4/libtool.m4: Make lt_ar_flags declare as quoted.

m4/libtool.m4

diff --git a/m4/libtool.m4 b/m4/libtool.m4
index 4ef92f3..75e666d 100644
--- a/m4/libtool.m4
+++ b/m4/libtool.m4
@@ -1577,7 +1577,7 @@
 
 test ${AR_FLAGS+y} || AR_FLAGS=${ARFLAGS-cr}
 lt_ar_flags=$AR_FLAGS
-_LT_DECL([], [lt_ar_flags], [0], [Flags to create an archive (by configure)])
+_LT_DECL([], [lt_ar_flags], [1], [Flags to create an archive (by configure)])
 
 # Make AR_FLAGS overridable by 'make ARFLAGS='.  Don't try to run-time override
 # by AR_FLAGS because that was never working and AR_FLAGS is about to die.