linux: add a "required" field to extension metadata

So downstream consumers don't need to maintain lists.

Author: indygreg

README.rst

@@ -358,6 +358,10 @@ extensions
    objs
       An array of paths to object files constituting this extension module.
 
+   required
+      Boolean indicating if this extension is required to initialize the Python
+      interpreter.
+
    static_lib
       The path to a static library defining this extension module. May not
       be defined.

cpython-linux/build.py

@@ -35,6 +35,17 @@
 LOG_PREFIX = [None]
 LOG_FH = [None]
 
+REQUIRED_EXTENSIONS = {
+    '_codecs',
+    '_io',
+    '_signal',
+    '_thread',
+    '_tracemalloc',
+    '_weakref',
+    'faulthandler',
+    'posix',
+}
+
 
 def log(msg):
     if isinstance(msg, bytes):
@@ -561,6 +572,10 @@ def process_setup_line(line, variant=None):
             'variant': 'default',
         })
 
+    for extension, entries in bi['extensions'].items():
+        for entry in entries:
+            entry['required'] = extension in REQUIRED_EXTENSIONS
+
     # Any paths left in modules_objs are not part of any extension and are
     # instead part of the core distribution.
     for p in sorted(modules_objs):