gh-105699: Use a Thread-Local Variable for PKGCONTEXT (gh-105740)

This fixes a race during import. The existing _PyRuntimeState.imports.pkgcontext is shared between interpreters, and occasionally this would cause a crash when multiple interpreters were importing extensions modules at the same time.  To solve this we add a thread-local variable for the value.  We also leave the existing state (and infrequent race) in place for platforms that do not support thread-local variables.

Tools/c-analyzer/c_parser/parser/_regexes.py

@@ -58,6 +58,7 @@ _KEYWORD = textwrap.dedent(r'''
             extern |
             register |
             static |
+            _Thread_local |
             typedef |
 
             const |
@@ -137,7 +138,7 @@ COMPOUND_TYPE_KIND = r'(?: \b (?: struct | union | enum ) \b )'
 #######################################
 # variable declarations
 
-_STORAGE = 'auto register static extern'.split()
+_STORAGE = 'auto register static extern _Thread_local'.split()
 STORAGE_CLASS = rf'(?: \b (?: {" | ".join(_STORAGE)} ) \b )'
 TYPE_QUALIFIER = r'(?: \b (?: const | volatile ) \b )'
 PTR_QUALIFIER = rf'(?: [*] (?: \s* {TYPE_QUALIFIER} )? )'

Tools/c-analyzer/c_parser/preprocessor/gcc.py

@@ -219,6 +219,7 @@ def _strip_directives(line, partial=0):
         line = line[m.end():]
 
     line = re.sub(r'__extension__', '', line)
+    line = re.sub(r'__thread\b', '_Thread_local', line)
 
     while (m := COMPILER_DIRECTIVE_RE.match(line)):
         before, _, _, closed = m.groups()