[embedded] Fix up lit.cfg and embedded/hello.swift's REQUIRES line

Author: kubamracek

test/embedded/hello.swift

@@ -2,6 +2,7 @@
 
 // REQUIRES: swift_in_compiler
 // REQUIRES: executable_test
+// REQUIRES: OS=macosx || OS=linux-gnu || OS=none-eabi || OS=none-elf
 
 print("Hello, Embedded Swift!")
 

test/lit.cfg

@@ -2105,6 +2105,10 @@ elif config.external_embedded_platform:
         config.swift_symbolgraph_extract,
         '-target', config.variant_triple,
         mcp_opt])
+    config.target_swift_synthesize_interface = ' '.join([
+        config.swift_synthesize_interface,
+        '-target', config.variant_triple,
+        mcp_opt])
     config.target_swift_ide_test = (
         '%s -target %s %s %s %s %s' %
         (config.swift_ide_test, config.variant_triple, config.resource_dir_opt,