[llvm] [offload] Add missing build dependency (PR #149326)

[via llvm-commits]

https://github.com/jprotze updated https://github.com/llvm/llvm-project/pull/149326

>From 9e300078186de3cf95a42c13ab5b8821b9f602e0 Mon Sep 17 00:00:00 2001
From: Joachim Jenke <jenke at itc.rwth-aachen.de>
Date: Thu, 17 Jul 2025 16:42:02 +0200
Subject: [PATCH] [offload] Add missing build dependency

libc++ headers must be generated before compiling part of liboffload.
The build error occurs if clang is configured to use libc++ by default.
Fixes issue #149324
---
 offload/tools/offload-tblgen/CMakeLists.txt | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/offload/tools/offload-tblgen/CMakeLists.txt b/offload/tools/offload-tblgen/CMakeLists.txt
index 15525dc44ea60..a5ae1c3757fbf 100644
--- a/offload/tools/offload-tblgen/CMakeLists.txt
+++ b/offload/tools/offload-tblgen/CMakeLists.txt
@@ -22,5 +22,11 @@ add_tablegen(offload-tblgen OFFLOAD
   RecordTypes.hpp
   )
 
+# Make sure that C++ headers are available, if libcxx is built at the same
+# time. This is important if clang is set to prefer libc++ over libstdc++
+if(TARGET cxx-headers)
+  add_dependencies(offload-tblgen cxx-headers)
+endif()
+
 set(OFFLOAD_TABLEGEN_EXE "${OFFLOAD_TABLEGEN_EXE}" CACHE INTERNAL "")
 set(OFFLOAD_TABLEGEN_TARGET "${OFFLOAD_TABLEGEN_TARGET}" CACHE INTERNAL "")