[Bug binutils/21702] New: MinGW ar cannot handle LTO object files when in MRI script mode

[spam.martin.schulze at gmx dot de]

https://sourceware.org/bugzilla/show_bug.cgi?id=21702

            Bug ID: 21702
           Summary: MinGW ar cannot handle LTO object files when in MRI
                    script mode
           Product: binutils
           Version: 2.28
            Status: UNCONFIRMED
          Severity: normal
          Priority: P2
         Component: binutils
          Assignee: unassigned at sourceware dot org
          Reporter: spam.martin.schulze at gmx dot de
  Target Milestone: ---

Created attachment 10239
  --> https://sourceware.org/bugzilla/attachment.cgi?id=10239&action=edit
Example project that exhibits the problem

This problem turned up while cross-compiling Qt 5.9.0 with LTO enabled.
ar gives the error "plugin needed to handle lto object" and generates an output
file which results in undefined reference errors when linked.

You can reproduce this by running make in the attached project tree. (Obviously
you need x86_64-w64-mingw32-{ar,gcc} for this to work.)
The run will result in the aformentioned errors instead of a successfully built
binary. The output is as follows:

$ make
x86_64-w64-mingw32-gcc -c -flto -o func.o func.c
x86_64-w64-mingw32-ar -M < mri_script
x86_64-w64-mingw32-ar: func.o: plugin needed to handle lto object
x86_64-w64-mingw32-gcc -flto main.c -o main -L. -lfunc
/tmp/cc7mkhTU.ltrans0.ltrans.o:<artificial>:(.text+0x1b): undefined reference
to `func'
/tmp/cc7mkhTU.ltrans0.ltrans.o:<artificial>:(.text+0x22): undefined reference
to `func2'

I also added a make target main.non-mri that uses command line parameters for
ar instead of the mri script. 
This invocation works as expected and builts an executable that can be run via
wine.

Additional Information:

I am running this on Arch Linux 64bit:

$ x86_64-w64-mingw32-ar --version
GNU ar (GNU Binutils) 2.28

I did not post this on MinGW bugtracker as they seem to only handle bugs under
Windows and this is a cross-compilation problem.
I also decided against the GCC bugtracker as this seems to be a problem with
the archiver.

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