meson: Don't pass -Werror to vendored code

Do it the correct way with libusrsctp -- override the option so that
it's done in a compiler-agnostic and future-proof way.

Part-of: <https://gitlab.freedesktop.org/gstreamer/gstreamer/-/merge_requests/2494>

subprojects/gst-plugins-bad/ext/sctp/usrsctp/meson.build

@@ -31,7 +31,6 @@ else
         '-Wno-missing-declarations',
         '-Wno-old-style-definition',
         '-Wno-redundant-decls',
-        '-Wno-error',
     ])
 endif
 
@@ -169,6 +168,7 @@ usrsctp_static = static_library('usrsctp-static', sources,
     c_args: compile_args,
     dependencies: dependencies,
     include_directories: include_dirs,
+    override_options: ['werror=false'],
     install: false)
 
 # Declare dependency

subprojects/gst-plugins-bad/sys/qsv/libmfx/meson.build

@@ -81,7 +81,8 @@ libmfx_static = static_library('libmfx-static',
   c_args : libmfx_extra_args,
   cpp_args : libmfx_extra_args,
   dependencies : libmfx_extra_deps,
-  include_directories : libmfx_incl
+  include_directories : libmfx_incl,
+  override_options: ['werror=false'],
 )
 
 libmfx_internal_dep = declare_dependency(