gh-1547: Recommend --config-cache for configure

Add ``--config-cache`` to all relevant ``./configure`` invocations in
the front page and setup-building guide, matching what the WASM
commands already do. Add a brief explanation noting that ``config.cache``
should be deleted when switching compilers or significantly changing
the build environment.

Author: johnslavik

getting-started/setup-building.rst

@@ -192,7 +192,12 @@ for development is to configure it and then compile it.
 
 Configuration is typically::
 
-   $ ./configure --with-pydebug
+   $ ./configure --config-cache --with-pydebug
+
+The ``--config-cache`` (``-C``) option speeds up repeated ``configure`` runs
+by caching results in a ``config.cache`` file. If you switch compilers or
+significantly change your build environment, delete ``config.cache`` before
+re-running ``configure``.
 
 More flags are available to ``configure``, but this is the minimum you should
 do to get a pydebug build of CPython.
@@ -283,7 +288,7 @@ to learn more about these options.
 
 .. code:: console
 
-   $ ./configure --enable-optimizations --with-lto
+   $ ./configure --config-cache --enable-optimizations --with-lto
 
 .. _windows-compiling:
 
@@ -864,7 +869,8 @@ some of CPython's modules (for example, ``zlib``).
 
             $ GDBM_CFLAGS="-I$(brew --prefix gdbm)/include" \
                GDBM_LIBS="-L$(brew --prefix gdbm)/lib -lgdbm" \
-               ./configure --with-pydebug \
+               ./configure --config-cache \
+                           --with-pydebug \
                            --with-openssl="$(brew --prefix openssl@3)"
 
       .. tab:: Python 3.10
@@ -873,7 +879,8 @@ some of CPython's modules (for example, ``zlib``).
 
             $ CPPFLAGS="-I$(brew --prefix gdbm)/include -I$(brew --prefix xz)/include" \
                LDFLAGS="-L$(brew --prefix gdbm)/lib -L$(brew --prefix xz)/lib" \
-               ./configure --with-pydebug \
+               ./configure --config-cache \
+                           --with-pydebug \
                            --with-openssl="$(brew --prefix openssl@3)" \
                            --with-tcltk-libs="$(pkg-config --libs tcl tk)" \
                            --with-tcltk-includes="$(pkg-config --cflags tcl tk)" \
@@ -895,7 +902,8 @@ some of CPython's modules (for example, ``zlib``).
 
             $ GDBM_CFLAGS="-I$(dirname $(dirname $(which port)))/include" \
                GDBM_LIBS="-L$(dirname $(dirname $(which port)))/lib -lgdbm" \
-               ./configure --with-pydebug \
+               ./configure --config-cache \
+                           --with-pydebug \
                            --with-system-libmpdec
 
       .. tab:: Python 3.11-3.12
@@ -904,7 +912,8 @@ some of CPython's modules (for example, ``zlib``).
 
             $ GDBM_CFLAGS="-I$(dirname $(dirname $(which port)))/include" \
                GDBM_LIBS="-L$(dirname $(dirname $(which port)))/lib -lgdbm" \
-               ./configure --with-pydebug
+               ./configure --config-cache \
+                           --with-pydebug
 
    And finally, run ``make``::
 

index.rst

@@ -43,13 +43,13 @@ instructions please see the :ref:`setup guide <setup>`.
 
       .. code-block:: shell
 
-         ./configure --with-pydebug && make -j $(nproc)
+         ./configure --config-cache --with-pydebug && make -j $(nproc)
 
    .. tab:: macOS
 
       .. code-block:: shell
 
-         ./configure --with-pydebug && make -j8
+         ./configure --config-cache --with-pydebug && make -j8
 
    .. tab:: Windows