Check all targets to find duplicated outputs.

Currently, GN doesn't find duplicated outputs between different
toolchain target. To fix this, I changed to see all_targets_ instead of
default_toolchain_targets_ for duplicated output error.

This is to fix error in
https://ci.chromium.org/ui/p/chromium/builders/try/ios-catalyst/2510/overview

With this CL error for the build config changed from

```
Two or more targets generate the same output:
  sdk/xcode_links/MacOSX26.0.sdk/usr/include/DarwinBasic.modulemap

This is can often be fixed by changing one of the target names, or by
setting an output_name on one of them.

Collisions:
  //buildtools/third_party/libc++:copy_sysroot_modulemaps(//build/toolchain/ios:ios_clang_x64)
```
to

```
Two or more targets generate the same output:
  sdk/xcode_links/MacOSX26.0.sdk/usr/include/DarwinBasic.modulemap

This is can often be fixed by changing one of the target names, or by
setting an output_name on one of them.

Collisions:
  //buildtools/third_party/libc++:copy_sysroot_modulemaps(//build/toolchain/ios:ios_clang_x64)
  //buildtools/third_party/libc++:copy_sysroot_modulemaps(//build/toolchain/mac:clang_arm64)
```

Change-Id: I6f95854c54f33c6809afc1cb43715e33f0677555
Reviewed-on: https://gn-review.googlesource.com/c/gn/+/19760
Reviewed-by: Sylvain Defresne <sdefresne@chromium.org>
Commit-Queue: Takuto Ikuta <tikuta@google.com>

src/gn/ninja_build_writer.cc

diff --git a/src/gn/ninja_build_writer.cc b/src/gn/ninja_build_writer.cc
index ca8ff17..d8d7c39 100644
--- a/src/gn/ninja_build_writer.cc
+++ b/src/gn/ninja_build_writer.cc
@@ -595,7 +595,7 @@
       const StringAtom output_string_atom(output_string);
 
       if (!written_rules.insert(output_string_atom).second) {
-        *err = GetDuplicateOutputError(default_toolchain_targets_, output);
+        *err = GetDuplicateOutputError(all_targets_, output);
         return false;
       }
     }