bpo-29643: Fix check for --enable-optimizations (GH-869)

The presence of the ``--enable-optimizations`` flag is indicated by the
value of ``$enableval``, but the configure script was checking ``$withval``,
resulting in the ``--enable-optimizations`` flag being effectively ignored.
(cherry picked from commit 8cea5929f5)

Misc/NEWS

@@ -60,6 +60,11 @@ Library
   exception) to exception(s) raised in the dispatched methods.
   Patch by Petr Motejlek.
 
+Build
+-----
+
+- bpo-29643: Fix ``--enable-optimization`` didn't work.
+
 
 What's New in Python 3.6.1?
 ===========================

configure

@@ -6521,7 +6521,7 @@ $as_echo_n "checking for --enable-optimizations... " >&6; }
 # Check whether --enable-optimizations was given.
 if test "${enable_optimizations+set}" = set; then :
   enableval=$enable_optimizations;
-if test "$withval" != no
+if test "$enableval" != no
 then
   Py_OPT='true'
   { $as_echo "$as_me:${as_lineno-$LINENO}: result: yes" >&5

configure.ac

@@ -1274,7 +1274,7 @@ Py_OPT='false'
 AC_MSG_CHECKING(for --enable-optimizations)
 AC_ARG_ENABLE(optimizations, AS_HELP_STRING([--enable-optimizations], [Enable expensive optimizations (PGO, etc).  Disabled by default.]),
 [
-if test "$withval" != no
+if test "$enableval" != no
 then
   Py_OPT='true'
   AC_MSG_RESULT(yes);