[llvm] [SystemZ][z/OS] Define _XOPEN_SOURCE=600 for dlopen (PR #127254)

[Abhina Sree via llvm-commits]

https://github.com/abhina-sree created https://github.com/llvm/llvm-project/pull/127254

On z/OS, dlopen is guarded by  _XOPEN_SOURCE=600 so define it when checking for the symbol.

>From 15ffcbc9283064ab848cdbdc27cd742a69807892 Mon Sep 17 00:00:00 2001
From: Abhina Sreeskantharajan <Abhina.Sreeskantharajan at ibm.com>
Date: Fri, 14 Feb 2025 15:05:34 -0500
Subject: [PATCH] define _XOPEN_SOURCE=600 to see dlopen

---
 llvm/cmake/config-ix.cmake | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/llvm/cmake/config-ix.cmake b/llvm/cmake/config-ix.cmake
index c128fd2ed125c..15ae04f5a6913 100644
--- a/llvm/cmake/config-ix.cmake
+++ b/llvm/cmake/config-ix.cmake
@@ -390,7 +390,14 @@ if (NOT PURE_WINDOWS)
   if( HAVE_LIBDL )
     list(APPEND CMAKE_REQUIRED_LIBRARIES dl)
   endif()
+  # Add the _XOPEN_SOURCE macro on z/OS, as certain test(s) use dlopen
+  if (ZOS)
+    list(APPEND CMAKE_REQUIRED_DEFINITIONS "-D_XOPEN_SOURCE=600")
+  endif()
   check_symbol_exists(dlopen dlfcn.h HAVE_DLOPEN)
+  if (ZOS)
+    list(REMOVE_ITEM CMAKE_REQUIRED_DEFINITIONS "-D_XOPEN_SOURCE=600")
+  endif()
   if( HAVE_LIBDL )
     list(REMOVE_ITEM CMAKE_REQUIRED_LIBRARIES dl)
   endif()