Add preliminary macOS support

Makefile

@@ -18,6 +18,10 @@ ifeq ($(_THEOS_FINAL_PACKAGE),$(_THEOS_TRUE))
 	$(ECHO_NOTHING)cp -a $(THEOS_OBJ_DIR)/dSYMs/Orion.framework.dSYM $(DSYM_DIR)$(ECHO_END)
 endif
 	$(ECHO_NOTHING)xcrun tapi stubify $(SDK_DIR)/Orion$(ECHO_END)
+	$(ECHO_NOTHING)if [[ -L $(SDK_DIR)/Orion ]]; then \
+		ln -s Versions/Current/Orion.tbd $(SDK_DIR)/Orion.tbd; \
+		rm $(SDK_DIR)/Versions/Current/Orion; \
+	fi$(ECHO_END)
 	$(ECHO_NOTHING)rm $(SDK_DIR)/Orion $(SDK_DIR)/Modules/Orion.swiftmodule/*.swiftmodule$(ECHO_END)
 	$(ECHO_NOTHING)rm -rf $(THEOS_STAGING_DIR)/Library/Frameworks/Orion.framework/{Headers,Modules}$(ECHO_END)
 

Orion.xcodeproj/project.pbxproj

@@ -510,7 +510,7 @@
 				);
 				MACOSX_DEPLOYMENT_TARGET = 10.14.4;
 				MARKETING_VERSION = 0.9.0;
-				OTHER_LDFLAGS = "-lsubstrate";
+				OTHER_LDFLAGS = "-weak-lsubstrate";
 				PRODUCT_BUNDLE_IDENTIFIER = dev.theos.orion;
 				PRODUCT_NAME = "$(TARGET_NAME:c99extidentifier)";
 				SKIP_INSTALL = NO;
@@ -557,7 +557,7 @@
 				);
 				MACOSX_DEPLOYMENT_TARGET = 10.14.4;
 				MARKETING_VERSION = 0.9.0;
-				OTHER_LDFLAGS = "-lsubstrate";
+				OTHER_LDFLAGS = "-weak-lsubstrate";
 				PRODUCT_BUNDLE_IDENTIFIER = dev.theos.orion;
 				PRODUCT_NAME = "$(TARGET_NAME:c99extidentifier)";
 				SKIP_INSTALL = NO;

Sources/OrionBackend_Substrate/SubstrateBackend.swift

@@ -12,6 +12,11 @@ extension Backends {
     /// if the target system has CydiaSubstrate – or another hooking
     /// framework which vends its API – installed, this backend makes
     /// for a sensible default choice.
+    ///
+    /// - Warning: Do not use this backend if the target system does not
+    /// have a framework which vends the CydiaSubstrate APIs. Doing so
+    /// will result in the process crashing with an "undefined symbols"
+    /// error.
     public struct Substrate: DefaultBackend {
         public init() {}
     }