Fix the logic to generate .pro file (#664)

* Fix the logic to generate .pro file

* update readme file

* modify the release notes

Co-authored-by: Cynthia Jiang <cynthiajiang@google.com>

Author: cynthiajoan

android_build_files/generate_proguard.gradle

@@ -44,6 +44,7 @@ def generateCppProguard(File library, String outCppPro) {
 //   proguardSet: The set of proguard files to use.
 //   outputProguard: The path to the output proguard file.
 def generateFinalProguard(Set<File> proguardSet, String outputProguard) {
+
   Set<String> proguardLineSet = new HashSet<String>()
   for (File pro : proguardSet) {
     for (String line : pro.text.split("[\\r\\n]+")) {
@@ -79,9 +80,12 @@ def defineGenerateProguardFile(String subproject, String buildType,
       Set<File> librarySet = fileTree("$nativeBuildDir")
           .matching({ include "**/*firebase_${subproject}*" }).getFiles()
       String cppProguard = "$buildDir/cpp_${subproject}.pro"
-      if (!librarySet.isEmpty()) {
+      while (!librarySet.isEmpty()) {
         File lib = librarySet.iterator().next()
-        generateCppProguard(lib, cppProguard)
+        librarySet.remove(lib)
+        if (lib.name.endsWith(".a")) {
+          generateCppProguard(lib, cppProguard)
+        }
       }
 
       // Combine the proguard files into a single file.

release_build_files/readme.md

@@ -570,6 +570,8 @@ code.
 ### 8.5.0
 -   Changes
     -   General: Updating Android and iOS dependencies to the latest.
+    -   General: Fix the generating of proguard file 
+        ([#664](https://github.com/firebase/firebase-cpp-sdk/pull/664)).
 
 ### 8.4.0
 -   Changes