Core Build local debug use launch environment attributes.

The Core Build local debug session uses the environment variables from
the environment tab that was added in eclipse-cdt#901.

dsf-gdb/org.eclipse.cdt.dsf.gdb/src/org/eclipse/cdt/dsf/gdb/internal/launching/CoreBuildLocalDebugLaunchDelegate.java

@@ -40,6 +40,7 @@
 import org.eclipse.debug.core.DebugException;
 import org.eclipse.debug.core.ILaunch;
 import org.eclipse.debug.core.ILaunchConfiguration;
+import org.eclipse.debug.core.ILaunchManager;
 import org.eclipse.launchbar.core.target.ILaunchTarget;
 import org.eclipse.launchbar.core.target.launch.ITargetedLaunch;
 
@@ -81,6 +82,14 @@ public void launch(ILaunchConfiguration configuration, String mode, ILaunch laun
 		envProps.putAll(buildEnv);
 		gdbLaunch.setInitialEnvironment(envProps);
 
+		// Override initial environment by launch configuration attributes.
+		Map<String, String> launchEnvironment = configuration.getAttribute(ILaunchManager.ATTR_ENVIRONMENT_VARIABLES,
+				new HashMap<>());
+		if (!configuration.getAttribute(ILaunchManager.ATTR_APPEND_ENVIRONMENT_VARIABLES, true)) {
+			envProps.clear();
+		}
+		envProps.putAll(launchEnvironment);
+
 		IToolChain toolChain = buildConfig.getToolChain();
 		Path gdbPath = toolChain.getCommandPath(Paths.get("gdb")); //$NON-NLS-1$
 		gdbLaunch.setGDBPath(gdbPath != null ? gdbPath.toString() : "gdb"); //$NON-NLS-1$