[Bug lto/101473] LTO makes debug info depend on toolchain path

["rguenth at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=101473

Richard Biener <rguenth at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|WAITING                     |NEW

--- Comment #5 from Richard Biener <rguenth at gcc dot gnu.org> ---
Confirmed.  The difference is

--- t2.g        2021-07-19 15:17:18.856725031 +0200
+++ t1.g        2021-07-19 15:17:20.632748927 +0200
@@ -1387,20 +1387,20 @@
  The Directory Table (offset 0x167, lines 5, columns 1):
   Entry        Name
   0    (indirect line string, offset: 0x0): /tmp
-  1    (indirect line string, offset: 0x16):
/tmp/install_alternate_two/usr/local/lib64/gcc/x86_64-pc-linux-gnu/12.0.0/include
-  2    (indirect line string, offset: 0x82): /usr/include/bits/types
-  3    (indirect line string, offset: 0x70): /usr/include/bits
-  4    (indirect line string, offset: 0x9a): /usr/include
+  1    (indirect line string, offset: 0x55):
/tmp/install_one/usr/local/lib64/gcc/x86_64-pc-linux-gnu/12.0.0/include
+  2    (indirect line string, offset: 0x3d): /usr/include/bits/types
+  3    (indirect line string, offset: 0x2b): /usr/include/bits
+  4    (indirect line string, offset: 0x16): /usr/include

where stddef.h is included from.  I wonder how we can avoid this difference
without making the DWARF "invalid" though.  stddef.h is provided by the
compiler.  Btw, this doesn't neeed -flto to trigger it's visible with
plain -g as well, it just doesn't end up in differences in the symbol
table without -flto but the debug info still differs.