mpfs/knsh: Add C++ support

[pussuw]

Increase the kernel stack size to 2K because it overflows when executing
dtors.

Summary

Adds CXX support for kernel mode in MPFS

Impact

MPFS only

Testing

mpfs icicle:knsh

[pussuw]

The build error is the same as here: apache/nuttx-apps#1171
I'll do rebase on Friday

[pussuw]

Don't think the CI error is my doing:

[chip/45701c0.zip]
  End-of-central-directory signature not found.  Either this file is not
  a zipfile, or it constitutes one disk of a multi-part archive.  In the
  latter case the central directory and zipfile comment will be found on
  the last disk(s) of this archive.
unzip:  cannot find zipfile directory in one of chip/45701c0.zip or
        chip/45701c0.zip.zip, and cannot find chip/45701c0.zip.ZIP, period.
make[1]: *** [chip/esp-wireless-drivers-3rdparty] Error 9
make[1]: Target `context' not remade because of errors.
make: *** [arch/xtensa/src/.context] Error 2
make: Target `all' not remade because of errors.
/Users/runner/work/incubator-nuttx/incubator-nuttx/sources/nuttx/tools/testbuild.sh: line 257: /Users/runner/work/incubator-nuttx/incubator-nuttx/sources/nuttx/../nuttx/nuttx.manifest: No such file or directory
  Normalize esp32-devkitc/wapi