Fix XDR hash check for ifdef-guarded XDR files

[leighmcculloch]

Fixes CI failures on #5148 by marking ifdef-guarded XDR files with an IFDEF_GUARDED sentinel so the hash check skips those files.

[leighmcculloch]

Closing - created by mistake, fix commit not pushed yet

[Copilot]

Pull request overview

Updates the build system and core code paths to support conditionally-compiled XDR variants (via --enable-xdr-* flags), addressing CI hash-check issues when XDR files are #ifdef-guarded.

Changes:

• Add configure-time flags and propagate -DXDR_* defines into XDR header generation.
• Add #ifdef-guarded handling for TransactionMeta v5 and LedgerEntry ext v2.
• Introduce an optional HelloWorld operation frame behind XDR_HELLO_WORLD.

Reviewed changes

Copilot reviewed 10 out of 10 changed files in this pull request and generated 3 comments.

Show a summary per file

File	Description
src/util/MetaUtils.cpp	Adds normalization support for TransactionMeta v5 under XDR_TRANSACTION_META_V5.
src/transactions/TransactionMeta.cpp	Adds v5 switch cases and selects meta version 5 when enabled.
src/transactions/OperationFrame.cpp	Conditionally wires up HELLO_WORLD operation and include.
src/transactions/HelloWorldOpFrame.h	Adds optional operation frame declaration guarded by XDR_HELLO_WORLD.
src/transactions/HelloWorldOpFrame.cpp	Adds optional operation frame implementation guarded by XDR_HELLO_WORLD.
src/protocol-curr/xdr	Updates XDR submodule reference.
src/invariant/LedgerEntryIsValid.cpp	Adjusts ledger entry ext-version checks and liquidity pool sponsorship logic under XDR_LEDGER_ENTRY_EXT_V2.
src/Makefile.am	Passes $(XDR_DEFINES) to XDR compiler; adds HelloWorld sources to build.
configure.ac	Introduces --enable-xdr-* options as automake conditionals.
common.mk	Adds XDR_DEFINES/AM_CPPFLAGS plumbing for the new XDR feature flags.

[Copilot]

HelloWorldOpFrame.cpp is entirely #ifdef XDR_HELLO_WORLD-guarded, so when the flag is off this can compile as an empty translation unit and may trigger -Wempty-translation-unit (often promoted to -Werror). Consider adding these sources under an Automake conditional (if XDR_HELLO_WORLD ... endif) so the .cpp is only compiled when the feature is enabled.

Suggested change

	stellar_core_SOURCES += transactions/HelloWorldOpFrame.h transactions/HelloWorldOpFrame.cpp
	if XDR_HELLO_WORLD
	stellar_core_SOURCES += transactions/HelloWorldOpFrame.h transactions/HelloWorldOpFrame.cpp
	endif

[Copilot]

With XDR_LEDGER_ENTRY_EXT_V2 enabled, this only flags ext version 1 as sponsored, but appears to allow ext version 2 liquidity pool entries to pass without triggering the sponsorship error. If sponsorship is intended to be rejected for all non-zero extension versions, the condition should remain equivalent to le.ext.v() != 0 (or explicitly handle v2 semantics). If v2 is valid-and-not-sponsored, the error message/logic should be updated to reflect what v1/v2 represent.

[Copilot]

Enabling XDR_TRANSACTION_META_V5 changes the emitted transaction meta version for the same protocol range (V_23+) from 4 to 5. That’s a behavioral/serialization change controlled purely by a build-time flag, which can lead to interoperability issues across nodes/consumers built with different flags. Consider gating version = 5 on an explicit protocol version that defines meta v5 (or a runtime config knob intended for experimental builds), rather than only on a compile-time define.

Suggested change

	#ifdef XDR_TRANSACTION_META_V5
	version = 5;
	#else
	version = 4;
	#endif
	version = 4;