Skip building the Synchronization library on embedded AVR for now.

Author: Carl Peto

stdlib/public/Synchronization/CMakeLists.txt

@@ -142,6 +142,11 @@ if(SWIFT_SHOULD_BUILD_EMBEDDED_STDLIB)
     list(GET list 0 arch)
     list(GET list 1 mod)
     list(GET list 2 triple)
+
+    # Disable the Synchronization library on AVR for now.
+    if("${arch}" MATCHES "avr")
+      continue()
+    endif()
 
     set(SWIFT_SDK_embedded_ARCH_${arch}_MODULE "${mod}")
     set(SWIFT_SDK_embedded_LIB_SUBDIR "embedded")