Document quick compile check steps

Author: jamesclement1776

Python/compile.c

@@ -137,7 +137,8 @@ compiler_setup(compiler *c, mod_ty mod, PyObject *filename,
     c->c_optimize = (optimize == -1) ? _Py_GetConfig()->optimization_level : optimize;
     c->c_save_nested_seqs = false;
 
-    if (!_PyAST_Preprocess(mod, arena, filename, c->c_optimize, merged, 0)) {
+    if (!_PyAST_Preprocess(mod, arena, filename,
+                           c->c_optimize, merged, 0, 1)) {
         return ERROR;
     }
     c->c_st = _PySymtable_Build(mod, filename, &c->c_future);
@@ -1518,7 +1519,8 @@ _PyCompile_AstPreprocess(mod_ty mod, PyObject *filename, PyCompilerFlags *cf,
     if (optimize == -1) {
         optimize = _Py_GetConfig()->optimization_level;
     }
-    if (!_PyAST_Preprocess(mod, arena, filename, optimize, flags, no_const_folding)) {
+    if (!_PyAST_Preprocess(mod, arena, filename,
+                           optimize, flags, no_const_folding, 1)) {
         return -1;
     }
     return 0;

README.rst

@@ -57,6 +57,12 @@ On Unix, Linux, BSD, macOS, and Cygwin::
 
 This will install Python as ``python3``.
 
+Quickly checking that a source change still compiles requires only the first
+two steps above: run ``./configure`` once (or reuse a previous build directory),
+then run ``make -j`` from the top level to rebuild the changed files.  If you
+want to be sure no stale artifacts interfere, run ``make clean`` before the
+``make`` step.
+
 You can pass many options to the configure script; run ``./configure --help``
 to find out more.  On macOS case-insensitive file systems and on Cygwin,
 the executable is called ``python.exe``; elsewhere it's just ``python``.