Copy file-level preamble to reactor-specific files

See
#1599 (comment)
for discussion

org.lflang/src/org/lflang/generator/c/CGenerator.java

@@ -657,7 +657,6 @@ private void generateCodeFor(
     ) throws IOException {
         startTimeStepIsPresentCount = 0;
         code.pr(generateDirectives());
-        code.pr(generateTopLevelPreambles());
         code.pr(new CMainFunctionGenerator(targetConfig).generateCode());
         // Generate code for each reactor.
         generateReactorDefinitions();
@@ -1043,6 +1042,7 @@ private void generateReactorClass(Reactor reactor) throws IOException {
         header.pr("#ifndef " + guardMacro);
         header.pr("#define " + guardMacro);
         generateReactorClassHeaders(reactor, headerName, header, src);
+        src.pr(generateTopLevelPreambles());
         generateUserPreamblesForReactor(reactor, src);
         generateReactorClassBody(reactor, header, src);
         header.pr("#endif // " + guardMacro);