[llvm] [AIX] use LIBPATH on AIX instead of LD_LIBRARY_PATH (PR #94602)

[Chen Zheng via llvm-commits]

https://github.com/chenzheng1030 created https://github.com/llvm/llvm-project/pull/94602

LD_LIBRARY_PATH will becomes invalid when LIBPATH is also set on AIX.

See below example on AIX:
```
$ldd a.out
a.out needs:
	 /usr/lib/libc.a(shr.o)
Cannot find libtest.a
	 /unix
	 /usr/lib/libcrypt.a(shr.o)

$./a.out
Could not load program ./a.out:
	Dependent module libtest.a could not be loaded.
Could not load module libtest.a.
System error: No such file or directory

$export LD_LIBRARY_PATH=$LD_LIBRARY_PATH:/tmp
$./a.out ; echo $?
10

$export LIBPATH=./
$./a.out ; echo $?  >>>>>> Now LD_LIBRARY_PATH is not used bu system loader
Could not load program ./a.out:
	Dependent module libtest.a could not be loaded.
Could not load module libtest.a.
System error: No such file or directory
```

This breaks many AIX LIT cases on our downstream buildbots which sets LIBPATH.

>From 97355f58cc094864213ac6e16acfa9e1b41f2281 Mon Sep 17 00:00:00 2001
From: Chen Zheng <czhengsz at cn.ibm.com>
Date: Thu, 6 Jun 2024 04:31:14 -0400
Subject: [PATCH] use LIBPATH on AIX instead of LD_LIBRARY_PATH

---
 llvm/utils/lit/lit/llvm/config.py | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/llvm/utils/lit/lit/llvm/config.py b/llvm/utils/lit/lit/llvm/config.py
index 1d4babc99984b..8d5da6b4f9dc0 100644
--- a/llvm/utils/lit/lit/llvm/config.py
+++ b/llvm/utils/lit/lit/llvm/config.py
@@ -588,7 +588,10 @@ def use_clang(
             if getattr(self.config, pp, None)
         ]
 
-        self.with_environment("LD_LIBRARY_PATH", lib_paths, append_path=True)
+        if sys.platform.startswith("aix"):
+            self.with_environment("LIBPATH", lib_paths, append_path=True)
+        else:
+            self.with_environment("LD_LIBRARY_PATH", lib_paths, append_path=True)
 
         shl = getattr(self.config, "llvm_shlib_dir", None)
         pext = getattr(self.config, "llvm_plugin_ext", None)