Guard include/cxx with CONFIG_LIBMINIABI for C++ builds

[arjav1528]

Fixes #18088

Summary

include/cxx was unconditionally added for all C++ builds when neither LIBCXX nor UCLIBCXX was selected. This incorrectly included CONFIG_LIBCXXTOOLCHAIN builds. include/cxx provides NuttX C++ ABI headers (like libcxxabi), not a full stdlib—using it with an external toolchain causes header conflicts (e.g. div_t/ldiv_t/lldiv_t via cstdlib/stdlib.h).
ETL logic unchanged.

Impact

• CONFIG_LIBCXXTOOLCHAIN + LIBSUPCXX_TOOLCHAIN: No longer adds include/cxx (fixes conflict)
• CONFIG_LIBMINIABI: Still adds include/cxx as before
• CONFIG_LIBCXX / CONFIG_UCLIBCXX: No change

Testing

Host: macOS (Darwin), arm64
Boards: xmc4800-relax:nsh, sim:cxxtest

Config	Result
xmc4800-relax:nsh (LIBCXXTOOLCHAIN)	Configure OK; build fails on ARM toolchain C++ headers (algorithm, math.h)—pre-existing, unrelated to this fix
sim:cxxtest (UCLIBCXX)	Configure OK; build fails on macOS sim host layer (timer_t, kill)—pre-existing platform issue, unrelated

Logic verified: CONFIG_UCLIBCXX uses include/uClibc++; this fix only affects the else branch (LIBCXXNONE/LIBCXXTOOLCHAIN). Full verification recommended in CI (Linux/Docker) with proper toolchain.

Logs

18088.txt
xmc4800_nsh_docker_build.txt

[arjav1528]

@xiaoxiang781216 could you restart the workflow, the failing workflow seems to be a timeout issue

[trns1997]

@arjav1528 C++ builds that use lib from toolchain will technically fail. Further investigation is required to provide a complete solution. See: #18088 (comment)

[linguini1]

Please attach the full test logs.

[arjav1528]

Please attach the full test logs.

done, also could you please restart the workflows

[trns1997]

@arjav1528 C++ builds that use lib from toolchain will technically fail. Further investigation is required to provide a complete solution. See: #18088 (comment)

@arjav1528 I recommend you test xmc4800 nsh build in a docker container. You should face the issue I mentioned in the issue

[arjav1528]

@arjav1528 C++ builds that use lib from toolchain will technically fail. Further investigation is required to provide a complete solution. See: #18088 (comment)

@arjav1528 I recommend you test xmc4800 nsh build in a docker container. You should face the issue I mentioned in the issue

@trns1997 I tested the xmc4800nsh build inside the CI docker container, as per your sugggestion. the build fails, which confirms the issue which you identified.
but the root cause is the bundled ARM toolchain in the image. main is the cstdlib and bits/stdabs.h which bypasses the nuttx's isystem and pulls in the toolchain's newlib stdlib.h direclty.
the failure is not caused by cxx being in the include path, so my PR is not related to this issue, it will happen regardless of the PR's changes, since the conflict is b/w nuttx's stdlib and toolchain's stdlib
btw I've attached the build logs in the PR description

[arjav1528]

so most probably its a timeout issue, can be fixed by restarting the workfllow
@linguini1 @xiaoxiang781216

[trns1997]

@arjav1528 C++ builds that use lib from toolchain will technically fail. Further investigation is required to provide a complete solution. See: #18088 (comment)

@arjav1528 I recommend you test xmc4800 nsh build in a docker container. You should face the issue I mentioned in the issue

@trns1997 I tested the xmc4800nsh build inside the CI docker container, as per your sugggestion. the build fails, which confirms the issue which you identified. but the root cause is the bundled ARM toolchain in the image. main is the cstdlib and bits/stdabs.h which bypasses the nuttx's isystem and pulls in the toolchain's newlib stdlib.h direclty. the failure is not caused by cxx being in the include path, so my PR is not related to this issue, it will happen regardless of the PR's changes, since the conflict is b/w nuttx's stdlib and toolchain's stdlib btw I've attached the build logs in the PR description

hmmm not sure the CI will pass, because the CI uses the same image :/ . So you do not have a choice but address this underlying issue. If i get time tomorrow i will look into it.

[arjav1528]

@arjav1528 C++ builds that use lib from toolchain will technically fail. Further investigation is required to provide a complete solution. See: #18088 (comment)

@arjav1528 I recommend you test xmc4800 nsh build in a docker container. You should face the issue I mentioned in the issue

@trns1997 I tested the xmc4800nsh build inside the CI docker container, as per your sugggestion. the build fails, which confirms the issue which you identified. but the root cause is the bundled ARM toolchain in the image. main is the cstdlib and bits/stdabs.h which bypasses the nuttx's isystem and pulls in the toolchain's newlib stdlib.h direclty. the failure is not caused by cxx being in the include path, so my PR is not related to this issue, it will happen regardless of the PR's changes, since the conflict is b/w nuttx's stdlib and toolchain's stdlib btw I've attached the build logs in the PR description

hmmm not sure the CI will pass, because the CI uses the same image :/ . So you do not have a choice but address this underlying issue. If i get time tomorrow i will look into it.

@trns1997 @linguini1 @simbit18 @xiaoxiang781216 do you guys have any idea why is arm2 queued since 1 day 😭