misc: Revert "scons: Remove -Werror for the gem5 v22.0 release"

This reverts commit 4df0d886df.
https://gem5-review.googlesource.com/c/public/gem5/+/60510

Change-Id: I0833b210c6dd46f77dc0ca0cc399e013efb2e7ca
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/60638
Maintainer: Bobby Bruce <bbruce@ucdavis.edu>
Tested-by: kokoro <noreply+kokoro@google.com>
Reviewed-by: Bobby Bruce <bbruce@ucdavis.edu>

SConstruct

@@ -418,6 +418,13 @@ for variant_path in variant_paths:
                     conf.CheckLinkFlag(
                             '-Wl,--thread-count=%d' % GetOption('num_jobs'))
 
+        # Treat warnings as errors but white list some warnings that we
+        # want to allow (e.g., deprecation warnings).
+        env.Append(CCFLAGS=['-Werror',
+                             '-Wno-error=deprecated-declarations',
+                             '-Wno-error=deprecated',
+                            ])
+
     else:
         error('\n'.join((
               "Don't know what compiler options to use for your compiler.",