gh-108223: Add --disable-gil to configure (gh-108227)

The `--disable-gil` flags does not do anything yet other than define the
Py_NOGIL macro. This is intended to support setting up additional
buildbots.

configure.ac

@@ -7126,6 +7126,21 @@ AC_ARG_ENABLE([test-modules],
 AC_MSG_RESULT([$TEST_MODULES])
 AC_SUBST([TEST_MODULES])
 
+# Check for --disable-gil
+# --disable-gil
+AC_MSG_CHECKING([for --disable-gil])
+AC_ARG_ENABLE([gil],
+  [AS_HELP_STRING([--disable-gil], [enable experimental support for running without the GIL (default is no)])],
+  [AS_VAR_IF([enable_gil], [yes], [disable_gil=no], [disable_gil=yes])], [disable_gil=no]
+)
+AC_MSG_RESULT([$disable_gil])
+
+if test "$disable_gil" = "yes"
+then
+  AC_DEFINE([Py_NOGIL], [1],
+            [Define if you want to disable the GIL])
+fi
+
 AC_DEFUN([PY_STDLIB_MOD_SET_NA], [
   m4_foreach([mod], [$@], [
     AS_VAR_SET([py_cv_module_]mod, [n/a])])

pyconfig.h.in

@@ -1609,6 +1609,9 @@
    SipHash13: 3, externally defined: 0 */
 #undef Py_HASH_ALGORITHM
 
+/* Define if you want to disable the GIL */
+#undef Py_NOGIL
+
 /* Define if you want to enable internal statistics gathering. */
 #undef Py_STATS