[BOLT][test] Resolve symlink for nm tool (NFC) (llvm#136722)

Handle the case where nm could be a symlink to llvm-nm.

Author: yozhu

bolt/test/link_fdata.py

@@ -9,6 +9,7 @@
 
 import argparse
 import os
+import shutil
 import subprocess
 import sys
 import re
@@ -85,7 +86,7 @@
             exit("ERROR: unexpected input:\n%s" % line)
 
 # Read nm output: <symbol value> <symbol type> <symbol name>
-is_llvm_nm = os.path.basename(args.nmtool) == "llvm-nm"
+is_llvm_nm = os.path.basename(os.path.realpath(shutil.which(args.nmtool))) == "llvm-nm"
 nm_output = subprocess.run(
     [
         args.nmtool,