RFR: JDK-8323008: filter out any -std* flags added by autoconf from CC/CXX

[Magnus Ihse Bursie]

On Mon, 8 Jan 2024 10:16:21 GMT, Matthias Baesken <mbaesken at openjdk.org> wrote:

> It was observed, that autoconf 2.72 added on macOS x86_64 the flag -std=gnu++11 by default to CXX in the configure process .
> This is not really wanted so better remove / filter out any -std* flags added by autoconf from CC/CXX .
> 
> Seems we have something similar for some time for CFLAGS and CXXFLAGS ( see TOOLCHAIN_POST_DETECTION in make/autoconf/toolchain.m4) that
>  dates back to JDK 9.
> 
> See the discussion about this issue : https://mail.openjdk.org/pipermail/build-dev/2024-January/042551.html

make/autoconf/toolchain.m4 line 395:

> 393:   # filter out some unwanted additions autoconf may add to CXX; we saw this on macOS with autoconf 2.72
> 394:   UTIL_GET_NON_MATCHING_VALUES(cxx_filtered, $CXX, -std=c++11 -std=gnu++11)
> 395:   if test "x$cxx_filtered" != x; then

Why this test? If CXX is empty, then xcc_filtered will be empty too, right? And if CXX is exactly `-std=c++11`, then this test will render cxx_filter empty too, which will not change CXX -- which I believe is not what you want?

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PR Review Comment: https://git.openjdk.org/jdk/pull/17301#discussion_r1448696597