scons: Get rid of a flag which makes Werror optional.

This flag wasn't being used. Also move the Werror code to the
SConstruct now that it's being applied universally.

Change-Id: I18b00d4b41bc1add9271ca299c020c14970a6926
Reviewed-on: https://gem5-review.googlesource.com/5982
Reviewed-by: Andreas Sandberg <andreas.sandberg@arm.com>
Reviewed-by: Nikos Nikoleris <nikos.nikoleris@arm.com>
Maintainer: Andreas Sandberg <andreas.sandberg@arm.com>

SConstruct

@@ -359,6 +359,13 @@ if main['GCC'] or main['CLANG']:
     shared_partial_flags = ['-r', '-nostdlib']
     main.Append(PSHLINKFLAGS=shared_partial_flags)
     main.Append(PLINKFLAGS=shared_partial_flags)
+
+    # Treat warnings as errors but white list some warnings that we
+    # want to allow (e.g., deprecation warnings).
+    main.Append(CCFLAGS=['-Werror',
+                         '-Wno-error=deprecated-declarations',
+                         '-Wno-error=deprecated',
+                        ])
 else:
     print termcap.Yellow + termcap.Bold + 'Error' + termcap.Normal,
     print "Don't know what compiler options to use for your compiler."