[llvm] [LLVM] Fix llvm-gpu-loader use in standalone (PR #132664)

[Tristan Ross via llvm-commits]

https://github.com/RossComputerGuy created https://github.com/llvm/llvm-project/pull/132664

Fixes the standalone builds of LLVM itself. In nixpkgs, we create a trimmed down copy of the LLVM monorepo for compatibility with older LLVM releases. We don't include libc in this copy which causes the `llvm-libc-common-utilities` target to not be defined. This causes `llvm-gpu-loader` to try linking to `llvm-libc-common-utilities` but fails due to the target not existing.

>From 6ea431c2ee8e73bf68f19c6145cd78ae81cb3902 Mon Sep 17 00:00:00 2001
From: Tristan Ross <tristan.ross at midstall.com>
Date: Sun, 23 Mar 2025 20:37:44 -0700
Subject: [PATCH] [LLVM] Fix llvm-gpu-loader use in standalone

---
 cmake/Modules/FindLibcCommonUtils.cmake | 2 +-
 llvm/tools/CMakeLists.txt               | 2 +-
 2 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/cmake/Modules/FindLibcCommonUtils.cmake b/cmake/Modules/FindLibcCommonUtils.cmake
index 95426c51a6041..ede2e79dea786 100644
--- a/cmake/Modules/FindLibcCommonUtils.cmake
+++ b/cmake/Modules/FindLibcCommonUtils.cmake
@@ -7,7 +7,7 @@
 #===--------------------------------------------------------------------===//
 
 if(NOT TARGET llvm-libc-common-utilities)
-  set(libc_path ${CMAKE_CURRENT_LIST_DIR}/../../libc)
+  set(libc_path ${LLVM_MAIN_SRC_DIR}/../libc)
   if (EXISTS ${libc_path} AND IS_DIRECTORY ${libc_path})
     add_library(llvm-libc-common-utilities INTERFACE)
     # TODO: Reorganize the libc shared section so that it can be included without
diff --git a/llvm/tools/CMakeLists.txt b/llvm/tools/CMakeLists.txt
index 9fe6f8c6b9c21..601376be08c64 100644
--- a/llvm/tools/CMakeLists.txt
+++ b/llvm/tools/CMakeLists.txt
@@ -9,7 +9,7 @@
 # traversing each directory.
 create_llvm_tool_options()
 
-if(NOT LLVM_COMPILER_IS_GCC_COMPATIBLE)
+if(NOT LLVM_COMPILER_IS_GCC_COMPATIBLE OR NOT TARGET llvm-libc-common-utilities)
   set(LLVM_TOOL_LLVM_GPU_LOADER_BUILD OFF)
 endif()