Add Module For Checking Atomic

Adds function for detection if linking against libatomic is
required.

CheckAtomic.cmake

@@ -0,0 +1,29 @@
+include(CheckCXXSourceCompiles)
+
+# Some toolchains require explicitly linking against libatomic
+#
+# If such linking is required, then this function sets the
+# value of result to "atomic". Otherwise it remains untouched.
+# This makes it so that the function only needs to be called once
+# per project.
+#
+# It can be used as follows:
+#
+# check_cxx_needs_atomic(LINK_ATOMIC)
+# target_link_libraries(foo PRIVATE ${LINK_ATOMIC})
+# ...
+# target_link_libraries(bar PRIVATE ${LINK_ATOMIC})
+#
+function(check_cxx_needs_atomic result)
+  check_cxx_source_compiles("
+#include <atomic>
+#include <cstdint>
+  int main() {
+    return std::atomic<uint64_t>(0).load();
+  }
+  " success)
+
+  if(NOT success)
+    set(${result} atomic PARENT_SCOPE)
+  endif()
+endfunction()