Fix podspecs building with C++ 14 (#39464)

Summary:
Pull Request resolved: https://github.com/facebook/react-native/pull/39464

We currently have 854 warnings emitted due to nested namespaces being a C++ 17 extension lol.

This sets the standard explicitly to C++ 20 in the specs emitting the warnings (mostly RCT-Text).

It is undesirable that we add hundreds of warnings to the CocoaPods build without signal. Our Buck build and OSS Android build both treat warnings as errors. But... that is for another day.

Changelog: [Intenrnal]

Reviewed By: cortinico

Differential Revision: D49303081

fbshipit-source-id: 1233e9d51426fb8dbd8ca39a771e2fef3d0df856

packages/react-native/Libraries/Text/React-RCTText.podspec

@@ -30,6 +30,7 @@ Pod::Spec.new do |s|
   s.preserve_paths         = "package.json", "LICENSE", "LICENSE-docs"
   s.header_dir             = "RCTText"
   s.framework              = ["MobileCoreServices"]
+  s.pod_target_xcconfig    = { "CLANG_CXX_LANGUAGE_STANDARD" => "c++20" }
 
   s.dependency "Yoga"
   s.dependency "React-Core/RCTTextHeaders", version

packages/react-native/ReactCommon/React-nativeconfig.podspec

@@ -27,6 +27,7 @@ Pod::Spec.new do |s|
   s.source                 = source
   s.source_files           = "react/config/*.{m,mm,cpp,h}"
   s.header_dir             = "react/config"
+  s.pod_target_xcconfig    = { "CLANG_CXX_LANGUAGE_STANDARD" => "c++20" }
 
   if ENV['USE_FRAMEWORKS']
     s.header_mappings_dir     = './'

packages/react-native/ReactCommon/react/renderer/graphics/React-graphics.podspec

@@ -51,7 +51,8 @@ Pod::Spec.new do |s|
 
   s.pod_target_xcconfig  = { "USE_HEADERMAP" => "NO",
                              "HEADER_SEARCH_PATHS" => header_search_paths.join(" "),
-                             "DEFINES_MODULE" => "YES" }
+                             "DEFINES_MODULE" => "YES",
+                             "CLANG_CXX_LANGUAGE_STANDARD" => "c++20" }
 
   s.dependency "glog"
   s.dependency "RCT-Folly/Fabric", folly_version

packages/react-native/ReactCommon/reactperflogger/React-perflogger.podspec

@@ -31,4 +31,5 @@ Pod::Spec.new do |s|
   s.source                 = source
   s.source_files           = "**/*.{cpp,h}"
   s.header_dir             = "reactperflogger"
+  s.pod_target_xcconfig    = { "CLANG_CXX_LANGUAGE_STANDARD" => "c++20" }
 end