gh-98718: re-use already calculated is_python_build from getpath

Author: FFY00

Lib/sysconfig.py

@@ -221,12 +221,9 @@ def is_python_build(check_home=None):
         import warnings
         warnings.warn("check_home argument is deprecated and ignored.",
                       DeprecationWarning, stacklevel=2)
-    for fn in ("Setup", "Setup.local"):
-        if os.path.isfile(os.path.join(_PROJECT_BASE, "Modules", fn)):
-            return True
-    return False
+    return sys._is_python_build
 
-_PYTHON_BUILD = is_python_build()
+_PYTHON_BUILD = sys._is_python_build
 
 if _PYTHON_BUILD:
     for scheme in ('posix_prefix', 'posix_home'):

Python/sysmodule.c

@@ -3304,6 +3304,9 @@ _PySys_UpdateConfig(PyThreadState *tstate)
         SET_SYS_FROM_WSTR(SYS_ATTR, WSTR); \
     }
 
+#define COPY_BOOL(KEY, VALUE) \
+        SET_SYS(KEY, PyBool_FromLong(VALUE));
+
     if (config->module_search_paths_set) {
         COPY_LIST("path", config->module_search_paths);
     }
@@ -3315,6 +3318,7 @@ _PySys_UpdateConfig(PyThreadState *tstate)
     COPY_WSTR("exec_prefix", config->exec_prefix);
     COPY_WSTR("base_exec_prefix", config->base_exec_prefix);
     COPY_WSTR("platlibdir", config->platlibdir);
+    COPY_BOOL("_is_python_build", config->_is_python_build);
 
     if (config->pycache_prefix != NULL) {
         SET_SYS_FROM_WSTR("pycache_prefix", config->pycache_prefix);