Update C++ podspec

gRPC-C++.podspec

@@ -663,9 +663,9 @@ Pod::Spec.new do |s|
   end
 
   s.prepare_command = <<-END_OF_COMMAND
-    find src/cpp/ -type f -exec sed -E -i'.back' 's;#include "third_party/nanopb/(.*)";#include <nanopb/\\1>;g' {} \\\;
-    find src/cpp/ -name "*.back" -type f -delete
-    find src/core/ -regex ".*\.h" -type f -exec sed -E -i'.back' 's;#include "third_party/nanopb/(.*)";#include <nanopb/\\1>;g' {} \\\;
-    find src/core/ -name "*.back" -type f -delete
+    find src/cpp/ -type f ! -path '*.grpc_back' -print0 | xargs -0 -L1 sed -E -i'.grpc_back' 's;#include "(pb(_.*)?\\.h)";#include <nanopb/\\1>;g'
+    find src/cpp/ -type f -path '*.grpc_back' -print0 | xargs -0 rm
+    find src/core/ -type f ! -path '*.grpc_back' -print0 | xargs -0 -L1 sed -E -i'.grpc_back' 's;#include "(pb(_.*)?\\.h)";#include <nanopb/\\1>;g'
+    find src/core/ -type f -path '*.grpc_back' -print0 | xargs -0 rm
   END_OF_COMMAND
 end

templates/gRPC-C++.podspec.template

@@ -196,9 +196,9 @@
     end
 
     s.prepare_command = <<-END_OF_COMMAND
-      find src/cpp/ -type f -exec sed -E -i'.back' 's;#include "third_party/nanopb/(.*)";#include <nanopb/\\1>;g' {} \\\;
-      find src/cpp/ -name "*.back" -type f -delete
-      find src/core/ -regex ".*\.h" -type f -exec sed -E -i'.back' 's;#include "third_party/nanopb/(.*)";#include <nanopb/\\1>;g' {} \\\;
-      find src/core/ -name "*.back" -type f -delete
+      find src/cpp/ -type f ! -path '*.grpc_back' -print0 | xargs -0 -L1 sed -E -i'.grpc_back' 's;#include "(pb(_.*)?\\.h)";#include <nanopb/\\1>;g'
+      find src/cpp/ -type f -path '*.grpc_back' -print0 | xargs -0 rm
+      find src/core/ -type f ! -path '*.grpc_back' -print0 | xargs -0 -L1 sed -E -i'.grpc_back' 's;#include "(pb(_.*)?\\.h)";#include <nanopb/\\1>;g'
+      find src/core/ -type f -path '*.grpc_back' -print0 | xargs -0 rm
     END_OF_COMMAND
   end