fuzz.sh: use set -x to make the `west build ...` command visible

Users want to know what exactly failed.

Signed-off-by: Marc Herbert <marc.herbert@intel.com>

scripts/fuzz.sh

@@ -80,8 +80,12 @@ main()
     -DCONFIG_ASAN=y
   )
 
+  (set -x
+   # When passing conflicting -DVAR='VAL UE1' -DVAR='VAL UE2' to CMake,
+   # the last 'VAL UE2' wins. Previous ones are silently ignored.
   west build -d build-fuzz -b native_posix "$SOF_TOP"/app/ -- \
       "${fuzz_configs[@]}" "$@"
+  )
 
   if $BUILD_ONLY; then
       exit 0