GMP test fails with -flto

[Vincent Lefevre]

On 2019-07-01 16:36:23 +0200, Torbjorn Granlund wrote:
> Vincent Lefevre <vincent at vinc17.net> writes:
> 
>   I suggest another solution:
> 
>   First try like now. If the format is unknown, check whether the
>   object file contains the string ".gnu.lto" (which should mean
>   that GCC was used with LTO), and in this case, try again with
>   "-fno-lto" as the patch was doing.
> 
> That might work, but it is a bit more complex that ideally.  I believe
> some grep commands do not cope well with binaries.

Alternatively or additionally, use strings + grep (strings is part
of POSIX and first appeared in Issue 4; however it is not listed
in the GNU Coding Standards).

Otherwise "od -b" with awk, possibly in the same awk script as the
detection itself.

> I have forgotten why lto hurts the GMP_C_DOUBLE_FORMAT test.  (That's
> the problematic test, right?)

Yes, with LTO, the object file does not contain the structure as is.
Thus the detection from "od -b conftest.$OBJEXT" does not work.

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