Include system environment when debugging core build

When doing a local launch, the only environment passed to the debuggee
was the modified variables, typically just PATH. This meant all the
other environment was lost.

This change does the same thing as all the other calls to setBuildEnvironment
and passes in the initial system environment.

I added a small note to the API of setBuildEnvironment to try
to avoid this error in the future.

Author: jonahgraham

core/org.eclipse.cdt.core/src/org/eclipse/cdt/core/build/ICBuildConfiguration.java

@@ -151,6 +151,9 @@ default IBinary[] getBuildOutput() throws CoreException {
 	 * @param env
 	 *            build environment
 	 * @since 6.1
+	 * @implNote Ensure you pass a new non-empty map containing the base environment
+	 * as this method modifies the passed in map adding the ICBuildConfiguration specific
+	 * overrides, such as applying the project's build environment.
 	 */
 	default void setBuildEnvironment(Map<String, String> env) {
 	}

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

@@ -34,6 +34,7 @@
 import org.eclipse.cdt.dsf.gdb.service.GdbDebugServicesFactory;
 import org.eclipse.cdt.dsf.gdb.service.command.IGDBControl;
 import org.eclipse.cdt.dsf.service.DsfServicesTracker;
+import org.eclipse.cdt.utils.spawner.EnvironmentReader;
 import org.eclipse.core.runtime.CoreException;
 import org.eclipse.core.runtime.IProgressMonitor;
 import org.eclipse.core.runtime.IStatus;
@@ -76,10 +77,20 @@ public void launch(ILaunchConfiguration configuration, String mode, ILaunch laun
 		ILaunchTarget target = ((ITargetedLaunch) launch).getLaunchTarget();
 		ICBuildConfiguration buildConfig = getBuildConfiguration(configuration, mode, target, monitor);
 
-		Map<String, String> buildEnv = new HashMap<>();
-		buildConfig.setBuildEnvironment(buildEnv);
+		Map<String, String> systemEnv = new HashMap<>();
+		Properties environmentVariables = EnvironmentReader.getEnvVars();
+		for (String key : environmentVariables.stringPropertyNames()) {
+			String value = environmentVariables.getProperty(key);
+			systemEnv.put(key, value);
+		}
+
+		var before = new HashMap<>(systemEnv);
+		buildConfig.setBuildEnvironment(systemEnv);
+
+		before.forEach((k, v) -> systemEnv.remove(k, v));
+
 		Properties envProps = new Properties();
-		envProps.putAll(buildEnv);
+		envProps.putAll(systemEnv);
 		gdbLaunch.setInitialEnvironment(envProps);
 
 		String debugger = configuration.getAttribute(IGDBLaunchConfigurationConstants.ATTR_DEBUG_NAME,