[cmake] Set SWIFT_STDLIB_HAS_COMMANDLINE

Set the SWIFT_STDLIB_HAS_COMMANDLINE macro when the stdlib has command
line support. This is needed while building SwiftCore to ensure that it
exports the appropriate symbols.

Author: etcwilde

Runtimes/Core/CommandLineSupport/CMakeLists.txt

@@ -3,6 +3,8 @@ if(SwiftCore_ENABLE_COMMANDLINE_SUPPORT)
   target_include_directories(swiftCommandLineSupport PRIVATE
     "${SwiftCore_SWIFTC_SOURCE_DIR}/include"
     "${PROJECT_BINARY_DIR}/include")
+  target_compile_definitions(swiftCommandLineSupport PUBLIC
+    -DSWIFT_STDLIB_HAS_COMMANDLINE)
 
   target_link_libraries(swiftCommandLineSupport PRIVATE
     swiftShims)