Build fixes for roll (flutter/engine#135)

* Add define for rendering

* Fix metal enum for older SDKs, add missing dep

engine/src/flutter/impeller/BUILD.gn

@@ -13,6 +13,10 @@ config("impeller_public_config") {
     defines += [ "IMPELLER_SUPPORTS_PLATFORM=1" ]
   }
 
+  if (impeller_supports_rendering) {
+    defines += [ "IMPELLER_SUPPORTS_RENDERING=1" ]
+  }
+
   if (is_win) {
     defines += [ "_USE_MATH_DEFINES" ]
   }

engine/src/flutter/impeller/entity/BUILD.gn

@@ -87,6 +87,7 @@ impeller_component("entity_unittests") {
 
   deps = [
     ":entity",
+    "../geometry:geometry_unittests",
     "../playground",
   ]
 }

engine/src/flutter/impeller/renderer/backend/metal/command_buffer_mtl.mm

@@ -53,6 +53,18 @@ static CommandBuffer::Status ToCommitResult(MTLCommandBufferStatus status) {
   return CommandBufferMTL::Status::kError;
 }
 
+// TODO(dnfield): remove this declaration when we no longer need to build on
+// machines with lower SDK versions than 11.0.s
+#if !defined(MAC_OS_X_VERSION_11_0) || MAC_OS_X_VERSION_MAX_ALLOWED < MAC_OS_X_VERSION_11_0
+typedef enum MTLCommandEncoderErrorState : NSInteger {
+  MTLCommandEncoderErrorStateUnknown = 0,
+  MTLCommandEncoderErrorStateCompleted = 1,
+  MTLCommandEncoderErrorStateAffected = 2,
+  MTLCommandEncoderErrorStatePending = 3,
+  MTLCommandEncoderErrorStateFaulted = 4,
+} API_AVAILABLE(macos(11.0), ios(14.0));
+#endif
+
 API_AVAILABLE(ios(14.0), macos(11.0))
 NSString* MTLCommandEncoderErrorStateToString(
     MTLCommandEncoderErrorState state) {