improve alignment autoconf test (#1129) (#1139)

Replace the deprecated AC_TRY_RUN with AC_RUN_IFELSE. Also, standardize the
variable name and allow for caching of the result.
diff --git a/configure.ac b/configure.ac
index 6b331d5..2c8e246 100644
--- a/configure.ac
+++ b/configure.ac
@@ -2696,7 +2696,8 @@
 
 # check for systems that require aligned memory access
 AC_MSG_CHECKING(aligned memory access is required)
-AC_TRY_RUN([
+AC_CACHE_VAL(ac_cv_aligned_required,
+[AC_RUN_IFELSE([AC_LANG_SOURCE([[
 int main()
 {
     char s[16];
@@ -2708,18 +2709,16 @@
     if (*p1 == *p2)
         return 1;
     return 0;
-}
-              ],
-     [aligned_required=no],
-     [aligned_required=yes],
-     [aligned_required=yes])
-
-if test "$aligned_required" = yes ; then
+}]])],
+[ac_cv_aligned_required=no],
+[ac_cv_aligned_required=yes],
+[ac_cv_aligned_required=yes])
+])
+AC_MSG_RESULT($ac_cv_aligned_required)
+if test "$ac_cv_aligned_required" = yes ; then
   AC_DEFINE([HAVE_ALIGNED_REQUIRED], [1],
     [Define if aligned memory access is required])
 fi
-AC_MSG_RESULT($aligned_required)
-
 
 # str, bytes and memoryview hash algorithm
 AH_TEMPLATE(Py_HASH_ALGORITHM,