cmake : error when LLAMA_BUILD_APP=ON and LLAMA_BUILD_TOOLS=OFF

[Pento95]

Overview

LLAMA_BUILD_APP=ON silently fails to compile when LLAMA_BUILD_TOOLS=OFF because the app/ targets depend on impl targets defined in tools/ (e.g. llama-server-impl, llama-cli-impl). The error manifests as a missing build-info.h header, which is misleading and hard to diagnose.

This PR adds an explicit FATAL_ERROR when the incompatible combination is used, so the user gets a clear message instead of a cryptic compiler error.

Additional information

Tested with CMake 4.3.0 on Fedora 44 (Linux 7.0.9-205.fc44.x86_64).
With LLAMA_BUILD_APP=ON and LLAMA_BUILD_TOOLS=OFF, CMake now exits immediately with:
LLAMA_BUILD_APP requires LLAMA_BUILD_TOOLS to be enabled

Requirements

• I have read and agree with the contributing guidelines
• AI usage disclosure: YES — I used Claude Code (claude.ai/code) to help identify the root cause of the issue and suggest the fix (see below, "alternative fix"). The small fix and this description were written and reviewed by me.

Alternative fix

Claude suggested a more user-friendly approach:
if (LLAMA_BUILD_APP AND NOT LLAMA_BUILD_TOOLS)
message(WARNING "LLAMA_BUILD_APP requires LLAMA_BUILD_TOOLS, enabling it automatically")
set(LLAMA_BUILD_TOOLS ON CACHE BOOL "" FORCE)
endif()