[llvm] [UpdateTestChecks] Fix %update_mc_test_checks substitution (PR #172230)

[Alexander Richardson via llvm-commits]

https://github.com/arichardson created https://github.com/llvm/llvm-project/pull/172230

We need to explicitly pass --llvm-mc-binary to avoid picking up llvm-mc
from somewhere else in $PATH. Noticed this because test lines were being
generated that didn't include my latest changes to update_mc_test_checks.py


>From 76817c0f857d0961daeb6f4da4a5864956c378dc Mon Sep 17 00:00:00 2001
From: Alex Richardson <alexrichardson at google.com>
Date: Sun, 14 Dec 2025 13:59:35 -0800
Subject: [PATCH] =?UTF-8?q?[=F0=9D=98=80=F0=9D=97=BD=F0=9D=97=BF]=20initia?=
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Created using spr 1.3.8-beta.1
---
 llvm/test/tools/UpdateTestChecks/lit.local.cfg | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/llvm/test/tools/UpdateTestChecks/lit.local.cfg b/llvm/test/tools/UpdateTestChecks/lit.local.cfg
index 3c7aeb7fcd35a..7b347e4f319e8 100644
--- a/llvm/test/tools/UpdateTestChecks/lit.local.cfg
+++ b/llvm/test/tools/UpdateTestChecks/lit.local.cfg
@@ -56,4 +56,5 @@ if os.path.isfile(split_file_path):
 
 llvm_mc_path = os.path.join(config.llvm_tools_dir, "llvm-mc")
 if os.path.isfile(llvm_mc_path):
-    add_update_script_substitution("%update_mc_test_checks")
+    llvm_mc_arg = "--llvm-mc-binary " + shell_quote(llvm_mc_path)
+    add_update_script_substitution("%update_mc_test_checks", extra_args=llvm_mc_arg)