Updated all necessary libraries to use ROOT_ATOMIC_LIBS.

Whichever library was missing a link against libatomic in my
Raspberry Pi test build, received a link against ROOT_ATOMIC_LIBS
in this update.

io/io/CMakeLists.txt

@@ -54,6 +54,7 @@ ROOT_LINKER_LIBRARY(RIO
   $<TARGET_OBJECTS:RootPcmObjs>
   LIBRARIES
     ${CMAKE_DL_LIBS}
+    ${ROOT_ATOMIC_LIBS}
   DEPENDENCIES
     Core
     Thread

net/net/CMakeLists.txt

@@ -100,6 +100,8 @@ ROOT_STANDARD_LIBRARY_PACKAGE(Net
     -writeEmptyRootPCM
   DEPENDENCIES
     RIO
+  LIBRARIES
+    ${ROOT_ATOMIC_LIBS}
 )
 
 if(ssl)

proof/proof/CMakeLists.txt

@@ -86,4 +86,6 @@ ROOT_STANDARD_LIBRARY_PACKAGE(Proof
     RIO
     Thread
     Tree
+  LIBRARIES
+    ${ROOT_ATOMIC_LIBS}
 )

tree/tree/CMakeLists.txt

@@ -119,6 +119,8 @@ ROOT_STANDARD_LIBRARY_PACKAGE(Tree
     Imt
     Net
     RIO
+  LIBRARIES
+    ${ROOT_ATOMIC_LIBS}
 )
 
 ROOT_ADD_TEST_SUBDIRECTORY(test)