OpenJDK11 build on macOS with autoconf 2.72 / -std=gnu++11 option

[erik.joelsson at oracle.com]

On 1/3/24 13:03, Kim Barrett wrote:
>> On Jan 3, 2024, at 7:16 AM, Baesken, Matthias <matthias.baesken at sap.com> wrote:
>>
>> Btw.  I found  this rather recent discussion about   reverting the  forcing   of setting -std=gnu++11  in autoconf :
>>
>> https://urldefense.com/v3/__https://mail.gnu.org/archive/html/bug-autoconf/2023-12/msg00073.html__;!!ACWV5N9M2RV99hQ!KfFeVOARPmr8RlTN3t2qMgkljzWkcpqA_NwxnyMtkaHzz3dwDxZjVsZZZvQLEXP-Rd6rngZKnovzj0C6Uzn-XF_4Gw$
>> https://urldefense.com/v3/__https://savannah.gnu.org/support/?110879__;!!ACWV5N9M2RV99hQ!KfFeVOARPmr8RlTN3t2qMgkljzWkcpqA_NwxnyMtkaHzz3dwDxZjVsZZZvQLEXP-Rd6rngZKnovzj0C6Uzk4Umn7ug$
>>
>> revert forcing/setting -std=gnu++11 by default (introduced in Autoconf 2.70)
> So autoconf forcibly selects a -std= option, possibly overriding either an
> explicit option or the compiler's default.  Who thought that was a good idea?
> There are even comments from the time that question that "feature".
>
> It looks like there is code to attempt to deal with that sort of thing in our
> build system. See TOOLCHAIN_POST_DETECTION in make/autoconf/toolchain.m4. That
> dates back to JDK 9. However, that only deals with CFLAGS and CXXFLAGS. The
> AC_PROG_CC/CXX feature affects the CC/CXX variables. Bleh!

Looks like we need to extend this functionality and filter out any 
"-std*" flags added by autoconf from CC/CXX. Even if later "-std=c++14" 
on the command line overrides correctly, it would be good for 
sanitation. I think such a fix should be done in mainline to avoid 
different behavior with different versions of autoconf. It can then be 
backported to openjdk 11 to fix the more severe issue described here.

/Erik