Suppress subproject compile warnings

Question

I am using meson build system in my C++ project where I have several dependencies like DPDK, flatbuffers and so on as subprojects.

While compiling my project, I get spammed with tons of warnings from all the subproject codebases, like this:

../subprojects/dpdk/lib/eal/include/generic/rte_spinlock.h: In the function 'void rte_spinlock_recursive_lock(rte_spinlock_recursive_t*)':
../subprojects/dpdk/lib/eal/include/generic/rte_spinlock.h:233:14: warning: '++' expression of 'volatile' qualified type is deprecated [-Wvolatile].
  233 | slr->count++;
      | ~~~~~^~~~~

This swallows my own code warnings, which I would really like to fix.

I have tried

• to define the subproject with as_system() like this

  dpdk_dep = subproject('dpdk', default_options: dpdk_opt).get_variable('dpdk_dep').as_system('system')
  

• provided the --warnlevel' setting in the subproject configuration with 0' to disable all warnings

... but meson just ignores everything.

What am I doing wrong, or is this really a bug in meson?

I have tried to get support from the meson developers without success:

• https://github.com/mesonbuild/meson/issues/13611

There is even another ticket on this topic with no result: https://github.com/mesonbuild/meson/issues/11988

I also have a minimal example on github (see here: https://github.com/sla89/meson_isystem_dpdk) that can be used to reproduce the problem.