[libsupersize] Fix LTO detection for upcoming clang roll

This is a reland of the changes made in https://crrev.com/c/5254957 with
an additional fix to _DetectLto(...).

A consequence of llvm/llvm-project#78835 is that
map files will no longer include the lto cache directory (see maskray@'s
comment at https://g-issues.chromium.org/issues/41496774#comment17).
This CL updates libsupersize to support that new filename format.

Bug: 41496774
Change-Id: I8bc08cd8f54f7b241cd4a0d4f40879e640d03d04
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5277968
Reviewed-by: Andrew Grieve <[email protected]>
Commit-Queue: Alan Zhao <[email protected]>
Cr-Commit-Position: refs/heads/main@{#1258047}

Author: alanzhao1

tools/binary_size/libsupersize/linker_map_parser.py

@@ -563,7 +563,8 @@ def Parse(self, lines):
 
               is_partial = False
               cur_obj = None
-            elif cur_obj == 'lto.tmp' or 'thinlto-cache' in cur_obj:
+            elif (cur_obj == 'lto.tmp' or 'thinlto-cache' in cur_obj
+                  or '.lto.' in cur_obj):
               thin_map[address] = os.path.basename(cur_obj)
               cur_obj = None
 
@@ -670,8 +671,8 @@ def Parse(self, lines):
 def _DetectLto(lines):
   """Scans LLD linker map file and returns whether LTO was used."""
   # It's assumed that the first line in |lines| was consumed to determine that
-  # LLD was used. Seek 'thinlto-cache' prefix within an "indicator section" as
-  # indicator for LTO.
+  # LLD was used. Seek 'thinlto-cache' prefix or the string '.lto' within an
+  # "indicator section" as indicator for LTO.
   found_indicator_section = False
   # Potential names of "main section". Only one gets used.
   indicator_section_set = set(['.rodata', '.ARM.exidx'])
@@ -695,7 +696,7 @@ def _DetectLto(lines):
         found_indicator_section = True
     elif indent_size == 8:
       if found_indicator_section:
-        if tok.startswith('thinlto-cache'):
+        if tok.startswith('thinlto-cache') or '.lto.' in tok:
           return True
   return False