[Bug lto/110844] New: LTO sometimes fail with -save-temp -dumpdir options

["frankhb1989 at gmail dot com" <gcc-bugzilla@gcc.gnu.org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=110844

            Bug ID: 110844
           Summary: LTO sometimes fail with -save-temp -dumpdir options
           Product: gcc
           Version: 13.1.1
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: lto
          Assignee: unassigned at gcc dot gnu.org
          Reporter: frankhb1989 at gmail dot com
                CC: marxin at gcc dot gnu.org
  Target Milestone: ---

Cases:

$ cd /tmp
$ g++ --version
g++ (GCC) 13.1.1 20230714
Copyright (C) 2023 Free Software Foundation, Inc.
This is free software; see the source for copying conditions.  There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.

$ echo 'int main(){}' > a.cc
$ g++ -flto -c a.cc -o a.o
$ g++ -flto -save-temps -dumpdir . a.o
$ g++ -flto -c a.cc -o a.o -save-temps -dumpdir .
$ g++ -flto -save-temps -dumpdir . a.o
$ g++ -flto -save-temps -dumpdir /tmp/ a.o
/usr/sbin/ld: error: could not open arguments file
collect2: error: ld returned 1 exit status

The error message is from lto-plugin.c. Setting the environment variables 
(indicated by 'g++ -v' and then 'collect2 -v' from the result) properly, by "b
fopen if *(char*)$rsi == 'w'" for ld running in gdb a few times, it shows
something goes wrong in 'link_output_name' which forms 'arguments_file_name':
the variable incorrectly contains all the remain characters in the command
line. (This is also reproduced in MSYS2 ld which has no debug symbols
distributed together, after changing $rsi to $rdx.) The parsing implementation
of '-dumpdir' arguments introduced in 1dedc12d186a110854537e1279b4e6c29f2df35a
then looks quite suspicious.