[lldb] Add a CMake option to build agains the Python limited API (#152034)

This adds a CMake option (which defaults to OFF) to force building
against the Python limited API. This makes iterating on #151617 easier
and eventually will prevent us from regressing this configuration.

Author: JDevlieghere

lldb/cmake/modules/LLDBConfig.cmake

@@ -68,6 +68,7 @@ add_optional_dependency(LLDB_ENABLE_FBSDVMCORE "Enable libfbsdvmcore support in
 option(LLDB_USE_ENTITLEMENTS "When codesigning, use entitlements if available" ON)
 option(LLDB_BUILD_FRAMEWORK "Build LLDB.framework (Darwin only)" OFF)
 option(LLDB_ENABLE_PROTOCOL_SERVERS "Enable protocol servers (e.g. MCP) in LLDB" ON)
+option(LLDB_ENABLE_PYTHON_LIMITED_API "Force LLDB to only use the Python Limited API (requires SWIG 4.2 or later)" OFF)
 option(LLDB_NO_INSTALL_DEFAULT_RPATH "Disable default RPATH settings in binaries" OFF)
 option(LLDB_USE_SYSTEM_DEBUGSERVER "Use the system's debugserver for testing (Darwin only)." OFF)
 option(LLDB_SKIP_STRIP "Whether to skip stripping of binaries when installing lldb." OFF)

lldb/include/lldb/Host/Config.h.cmake

@@ -45,6 +45,8 @@
 
 #cmakedefine01 LLDB_ENABLE_PYTHON
 
+#cmakedefine01 LLDB_ENABLE_PYTHON_LIMITED_API
+
 #cmakedefine01 LLDB_ENABLE_FBSDVMCORE
 
 #cmakedefine01 LLDB_EMBED_PYTHON_HOME

lldb/source/Plugins/ScriptInterpreter/Python/lldb-python.h

@@ -45,12 +45,20 @@ static llvm::Expected<bool> *g_fcxx_modules_workaround [[maybe_unused]];
 #include <locale>
 #endif
 
+#define LLDB_MINIMUM_PYTHON_VERSION 0x03080000
+
+#if LLDB_ENABLE_PYTHON_LIMITED_API
+// If defined, LLDB will be ABI-compatible with all Python 3 releases from the
+// specified one onward, and can use Limited API introduced up to that version.
+#define Py_LIMITED_API LLDB_MINIMUM_PYTHON_VERSION
+#endif
+
 // Include python for non windows machines
 #include <Python.h>
 
 // Provide a meaningful diagnostic error if someone tries to compile this file
 // with a version of Python we don't support.
-static_assert(PY_VERSION_HEX >= 0x03080000,
+static_assert(PY_VERSION_HEX >= LLDB_MINIMUM_PYTHON_VERSION,
               "LLDB requires at least Python 3.8");
 #endif