bpo-43774: Document configure options (GH-25283)

Add Doc/using/configure.rst documentation to document configure,
preprocessor, compiler and linker options.

Add a new section about the "Python debug build".
diff --git a/Doc/using/index.rst b/Doc/using/index.rst
index 4a45121..e1a3111 100644
--- a/Doc/using/index.rst
+++ b/Doc/using/index.rst
@@ -15,6 +15,7 @@
 
    cmdline.rst
    unix.rst
+   configure.rst
    windows.rst
    mac.rst
    editors.rst