vm: DRY *Config structs w.r.t. aflags using cfg_if

Use cfg_if to further reduce the scope of the code difference between
different flag configurations, removing the risk of differing APIs and
removing the duplication/boilerplate code, which increases the chance of
subtle differences going unnoticed.

This re-lands aosp/3253223 (commit 1879fb945f4a) which a minor change to
avoid a compiler warning (treated as error) for unused function
parameters.

Note: no functional change intended.

Test: banchan com.android.virt aosp_arm64 && m apps_only dist
Change-Id: I41d093deb0ba71164b3d76e96ab97549d4326480
diff --git a/android/vm/Android.bp b/android/vm/Android.bp
index c1d9b6b..ba8b416 100644
--- a/android/vm/Android.bp
+++ b/android/vm/Android.bp
@@ -16,6 +16,7 @@
         "libbinder_rs",
         "libclap",
         "libenv_logger",
+        "libcfg_if",
         "libglob",
         "libhypervisor_props",
         "liblibc",
diff --git a/android/vm/src/main.rs b/android/vm/src/main.rs
index f2c2fa4..609bbdf 100644
--- a/android/vm/src/main.rs
+++ b/android/vm/src/main.rs
@@ -75,14 +75,14 @@
 }
 
 impl CommonConfig {
-    #[cfg(network)]
     fn network_supported(&self) -> bool {
-        self.network_supported
-    }
-
-    #[cfg(not(network))]
-    fn network_supported(&self) -> bool {
-        false
+        cfg_if::cfg_if! {
+            if #[cfg(network)] {
+                self.network_supported
+            } else {
+                false
+            }
+        }
     }
 }
 
@@ -117,14 +117,14 @@
 }
 
 impl DebugConfig {
-    #[cfg(debuggable_vms_improvements)]
     fn enable_earlycon(&self) -> bool {
-        self.enable_earlycon
-    }
-
-    #[cfg(not(debuggable_vms_improvements))]
-    fn enable_earlycon(&self) -> bool {
-        false
+        cfg_if::cfg_if! {
+            if #[cfg(debuggable_vms_improvements)] {
+                self.enable_earlycon
+            } else {
+                false
+            }
+        }
     }
 }
 
@@ -158,34 +158,34 @@
 }
 
 impl MicrodroidConfig {
-    #[cfg(vendor_modules)]
     fn vendor(&self) -> Option<&PathBuf> {
-        self.vendor.as_ref()
+        cfg_if::cfg_if! {
+            if #[cfg(vendor_modules)] {
+                self.vendor.as_ref()
+            } else {
+                None
+            }
+        }
     }
 
-    #[cfg(not(vendor_modules))]
-    fn vendor(&self) -> Option<&PathBuf> {
-        None
-    }
-
-    #[cfg(vendor_modules)]
     fn gki(&self) -> Option<&str> {
-        self.gki.as_deref()
+        cfg_if::cfg_if! {
+            if #[cfg(vendor_modules)] {
+                self.gki.as_deref()
+            } else {
+                None
+            }
+        }
     }
 
-    #[cfg(not(vendor_modules))]
-    fn gki(&self) -> Option<&str> {
-        None
-    }
-
-    #[cfg(device_assignment)]
     fn devices(&self) -> &[PathBuf] {
-        &self.devices
-    }
-
-    #[cfg(not(device_assignment))]
-    fn devices(&self) -> &[PathBuf] {
-        &[]
+        cfg_if::cfg_if! {
+            if #[cfg(device_assignment)] {
+                &self.devices
+            } else {
+                &[]
+            }
+        }
     }
 }
 
@@ -236,35 +236,36 @@
 }
 
 impl RunAppConfig {
-    #[cfg(multi_tenant)]
     fn extra_apks(&self) -> &[PathBuf] {
-        &self.extra_apks
+        cfg_if::cfg_if! {
+            if #[cfg(multi_tenant)] {
+                &self.extra_apks
+            } else {
+                &[]
+            }
+        }
     }
 
-    #[cfg(not(multi_tenant))]
-    fn extra_apks(&self) -> &[PathBuf] {
-        &[]
-    }
-
-    #[cfg(llpvm_changes)]
     fn instance_id(&self) -> Result<PathBuf, Error> {
-        Ok(self.instance_id.clone())
+        cfg_if::cfg_if! {
+            if #[cfg(llpvm_changes)] {
+                Ok(self.instance_id.clone())
+            } else {
+                Err(anyhow!("LLPVM feature is disabled, --instance_id flag not supported"))
+            }
+        }
     }
 
-    #[cfg(not(llpvm_changes))]
-    fn instance_id(&self) -> Result<PathBuf, Error> {
-        Err(anyhow!("LLPVM feature is disabled, --instance_id flag not supported"))
-    }
-
-    #[cfg(llpvm_changes)]
     fn set_instance_id(&mut self, instance_id_file: PathBuf) -> Result<(), Error> {
-        self.instance_id = instance_id_file;
-        Ok(())
-    }
-
-    #[cfg(not(llpvm_changes))]
-    fn set_instance_id(&mut self, _: PathBuf) -> Result<(), Error> {
-        Err(anyhow!("LLPVM feature is disabled, --instance_id flag not supported"))
+        cfg_if::cfg_if! {
+            if #[cfg(llpvm_changes)] {
+                self.instance_id = instance_id_file;
+                Ok(())
+            } else {
+                let _ = instance_id_file;
+                Err(anyhow!("LLPVM feature is disabled, --instance_id flag not supported"))
+            }
+        }
     }
 }