Fix CUDA and HIP kde_cpp extension meson builds

meson defaults to a debug build, and this caused a problem where linking would fail with 'ptxas : Optimized debugging not supported'

steps/kernel_density_estimation_cpp/meson.build

@@ -1,4 +1,4 @@
-project('kde_app', 'cpp')
+project('kde_app', 'cpp', default_options: ['--buildtype=release'])
 
 sycl_feature_code = '''#include <iostream>
 using namespace std;