[ROCDL] Set relaxed buffer OOB mode (#24692)

Recent LLVM changes to ptr addrspace(7)/fat buffer lowering (LLVM PRs
https://github.com/llvm/llvm-project/pull/134329 and
https://github.com/llvm/llvm-project/pull/134734 ) mean that
underalligned loads from buffer pointers get devectorized unless
"relaxed mode" is enabled. IREE already has mitigations for the issues
that this OOB mode handles, so we must enable relaxed mode to prevent
severe regressions as seen in #24690.

Sadly there's no test for this one as we don't currently have tests for
the module translation and this is a hotfix so I want to keep it
minimal.

compiler/plugins/target/ROCM/ROCMTarget.cpp

diff --git a/compiler/plugins/target/ROCM/ROCMTarget.cpp b/compiler/plugins/target/ROCM/ROCMTarget.cpp
index 0b1d80f..f6cdb12 100644
--- a/compiler/plugins/target/ROCM/ROCMTarget.cpp
+++ b/compiler/plugins/target/ROCM/ROCMTarget.cpp
@@ -881,6 +881,12 @@
         // that our CI or users may not be prepared for.
         llvmModule->addModuleFlag(llvm::Module::Error,
                                   "amdhsa_code_object_version", abiVersion);
+
+        // Set the buffer OOB mode to "relaxed", since IREE does its own, more
+        // precise, mitigations for partially OOB buffer reads of underalligned
+        // vectors.
+        llvmModule->addModuleFlag(llvm::Module::Max, "amdgpu.buffer.oob.mode",
+                                  1);
       }
 
       for (llvm::Function &f : llvmModule->functions()) {