replace --with-optimizations references with --enable-optimizations in docs.

Doc/whatsnew/3.6.rst

@@ -1795,7 +1795,7 @@ Build and C API Changes
   yet a supported platform, the Python test suite runs on the Android emulator
   with only about 16 tests failures. See the Android meta-issue :issue:`26865`.
 
-* The ``--with-optimizations`` configure flag has been added. Turning it on
+* The ``--enable-optimizations`` configure flag has been added. Turning it on
   will activate expensive optimizations like PGO.
   (Original patch by Alecsandru Patrascu of Intel in :issue:`26539`.)
 

README

@@ -46,7 +46,7 @@ For example:
 (This will fail if you *also* built at the top-level directory.
 You should do a "make clean" at the toplevel first.)
 
-To get an optimized build of Python, "configure --with-optimizations" before
+To get an optimized build of Python, "configure --enable-optimizations" before
 you run make.  This sets the default make targets up to enable Profile Guided
 Optimization (PGO) and may be used to auto-enable Link Time Optimization (LTO)
 on some platforms.  For more details, see the sections bellow.