bpo-45847: Fix _crypt detection on Ubuntu (GH-29743)

Author: tiran

configure

@@ -15805,7 +15805,7 @@ save_LIBS=$LIBS
 
 
   CPPFLAGS="$LIBCRYPT_CFLAGS $CFLAGS"
-  LDFLAGS="$LIBCRYPT_LIBS $LDFLAGS"
+  LIBS="$LIBCRYPT_LIBS $LIBS"
   { $as_echo "$as_me:${as_lineno-$LINENO}: checking for crypt or crypt_r" >&5
 $as_echo_n "checking for crypt or crypt_r... " >&6; }
 if ${ac_cv_crypt_crypt+:} false; then :

configure.ac

@@ -4243,7 +4243,7 @@ PKG_CHECK_MODULES([LIBCRYPT], [libxcrypt >= 3.1.1], [
 
 WITH_SAVE_ENV([
   CPPFLAGS="$LIBCRYPT_CFLAGS $CFLAGS"
-  LDFLAGS="$LIBCRYPT_LIBS $LDFLAGS"
+  LIBS="$LIBCRYPT_LIBS $LIBS"
   AC_CACHE_CHECK([for crypt or crypt_r], [ac_cv_crypt_crypt], [
     AC_LINK_IFELSE([AC_LANG_PROGRAM([
         #ifdef HAVE_CRYPT_H