chore: add nix.gni fallback for non-Nix builds and fix compiler warnings

CMakeLists.txt previously required a nix.gni file (generated by the Nix
shell hook) containing platform-specific GN args. Builds outside Nix
failed with "file STRINGS file nix.gni cannot be read". Now falls back
to sensible defaults (is_clang=true, use_lld=false,
clang_use_chrome_plugins=false) when the file doesn't exist.

Also add default cases to two switch statements that triggered
-Wswitch-default warnings in rtc_ice_transport.cc and error_factory.cc.

Author: kevindhanna

CMakeLists.txt

@@ -185,7 +185,18 @@ set_target_properties(libc++abi PROPERTIES IMPORTED_OBJECTS_DEBUG "${libc++abi_o
 # M114: branch-heads/5735
 set(WEBRTC_REVISION branch-heads/5735)
 
-file(STRINGS nix.gni NIX_GN_GEN_ARGS)
+# nix.gni is generated by the Nix shell hook (shell.nix) with platform-specific
+# GN args like clang_base_path and mac_sdk_path. For non-Nix builds, create an
+# empty file or one with: is_clang=true\nuse_lld=false\nclang_use_chrome_plugins=false
+if(EXISTS "${CMAKE_SOURCE_DIR}/nix.gni")
+  file(STRINGS nix.gni NIX_GN_GEN_ARGS)
+else()
+  set(NIX_GN_GEN_ARGS
+    "is_clang=true"
+    "use_lld=false"
+    "clang_use_chrome_plugins=false"
+  )
+endif()
 list(APPEND GN_GEN_ARGS
   rtc_build_examples=false
   rtc_use_x11=false

src/interfaces/rtc_ice_transport.cc

@@ -172,6 +172,8 @@ Napi::Value RTCIceTransport::GetGatheringState(const Napi::CallbackInfo &info) {
     state = webrtc::PeerConnectionInterface::IceGatheringState::
         kIceGatheringComplete;
     break;
+  default:
+    break;
   }
   CONVERT_OR_THROW_AND_RETURN_NAPI(info.Env(), state, result, Napi::Value)
   return result;

src/node/error_factory.cc

@@ -7,6 +7,7 @@
  */
 #include "error_factory.hh"
 
+#include <cassert>
 #include <string>
 
 #include "src/converters.hh"
@@ -94,6 +95,9 @@ node_webrtc::ErrorFactory::DOMExceptionNameToString(DOMExceptionName name) {
     return "NetworkError";
   case kOperationError:
     return "OperationError";
+  default:
+    assert(false && "unhandled DOMExceptionName enum value");
+    return "UnknownError";
   }
 }