Make precompiled headers additionalInputs rather than nonModuleHeaders

This is an NFC.  Precompiled headers don't transitively propagate but
headers do (even nonModuleHeaders), so they are more appropriately in
additionalInputs.

RELNOTES: None
PiperOrigin-RevId: 282396395
diff --git a/src/main/java/com/google/devtools/build/lib/rules/objc/CompilationSupport.java b/src/main/java/com/google/devtools/build/lib/rules/objc/CompilationSupport.java
index 5719156..4fe7a17 100644
--- a/src/main/java/com/google/devtools/build/lib/rules/objc/CompilationSupport.java
+++ b/src/main/java/com/google/devtools/build/lib/rules/objc/CompilationSupport.java
@@ -352,7 +352,7 @@
             .setHeadersCheckingMode(semantics.determineHeadersCheckingMode(ruleContext));
 
     if (pchHdr != null) {
-      result.addNonModuleMapHeader(pchHdr);
+      result.addAdditionalInputs(ImmutableList.of(pchHdr));
     }
 
     if (getCustomModuleMap(ruleContext).isPresent() || !generateModuleMap) {