[gcc r10-9307] Fix LTO bootstrap on Windows

[Eric Botcazou <ebotcazou@gcc.gnu.org>]

https://gcc.gnu.org/g:4be929be0317b2baf1c67b430ad0a2fbaed05152

commit r10-9307-g4be929be0317b2baf1c67b430ad0a2fbaed05152
Author: Eric Botcazou <ebotcazou@adacore.com>
Date:   Thu Jan 28 11:31:35 2021 +0100

    Fix LTO bootstrap on Windows
    
    The latest fix introduced a comparison of executables and this cannot
    directly work on Windows because they are timestamped.  Moreover nobody
    sets $(exeext) at top level, at least on MinGW, so you get weird behavior
    because some tools add the implicit .exe suffix and others do not.
    
    contrib/
            PR lto/85574
            * compare-lto: Deal with PE-COFF executables specifically.

Diff:
---
 contrib/compare-lto | 21 ++++++++++++++++++++-
 1 file changed, 20 insertions(+), 1 deletion(-)

diff --git a/contrib/compare-lto b/contrib/compare-lto
index 17379e196a7..c0bb71c0765 100755
--- a/contrib/compare-lto
+++ b/contrib/compare-lto
@@ -32,7 +32,7 @@ case $1 in
 esac
 
 if test $# != 2; then
-  echo 'usage: compare-lto file1.o file2.o' >&2
+  echo 'usage: compare-lto file1 file2' >&2
   exit 1
 fi
 
@@ -101,6 +101,25 @@ else
     else
       status=1
     fi
+
+  # PE-COFF executables are timestamped so skip leading bytes for them.
+  else
+    case "$1" in
+      *.exe)
+        if cmp -i 256 "$1" "$2"; then
+          status=0
+        else
+          status=1
+        fi
+        ;;
+      *)
+        if test -f "$1.exe" && cmp -i 256 "$1.exe" "$2.exe"; then
+          status=0
+        else
+          status=1
+        fi
+        ;;
+    esac
   fi
 fi