supersize: Fix --toolprefix="" not being followed

tools/binary_size/libsupersize/archive.py

Index: tools/binary_size/libsupersize/archive.py
diff --git a/tools/binary_size/libsupersize/archive.py b/tools/binary_size/libsupersize/archive.py
index 3016dd96fb586a7c5eb4afccc1199b79869245d7..8fa685b732bce08ca60ae4d981b50114ef3a3752 100644
--- a/tools/binary_size/libsupersize/archive.py
+++ b/tools/binary_size/libsupersize/archive.py
@@ -549,7 +549,16 @@ def _SectionSizesFromElf(elf_path, tool_prefix):
 def _ArchFromElf(elf_path, tool_prefix):
   args = [tool_prefix + 'readelf', '-h', elf_path]
   stdout = subprocess.check_output(args)
-  return re.search('Machine:\s*(\S+)', stdout).group(1)
+  machine = re.search('Machine:\s*(.+)', stdout).group(1)
+  if machine == 'Intel 80386':
+    return 'x86'
+  if machine == 'Advanced Micro Devices X86-64':
+    return 'x64'
+  elif machine == 'ARM':
+    return 'arm'
+  elif machine == 'AArch64':
+    return 'arm64'
+  return machine
 
 
 def _ParseGnArgs(args_path):
@@ -664,9 +673,10 @@ def Run(args, parser):
 
       packed_section_name = None
       architecture = metadata[models.METADATA_ELF_ARCHITECTURE]
-      if architecture == 'ARM':
+      # Packing occurs enabled only arm32 & arm64.
+      if architecture == 'arm':
         packed_section_name = '.rel.dyn'
-      elif architecture == 'AArch64':
+      elif architecture == 'arm64':
         packed_section_name = '.rela.dyn'
 
       if packed_section_name: