compilation of 1.0.15 release on gcc-15

[tomhenderson]

ArchLinux gcc-15.1.1 pipeline build

per-commit-gcc-default: extends: .base-per-commit-compile stage: build variables: MODE: default COMPILER: g++

/builds/nsnam/ns-3-allinone/ns-3.45/contrib/netsimulyzer/model/optional.h:268:22: error: a template argument list is expected after a name prefixed by the template keyword [-Wmissing-template-arg-list-after-template-kw]
  268 |     m_value.template emplace(std::forward<Args>(args)...);
      |                      ^
1 error generated.

[bpe2]

I could only replicate this with clang version: 20.1.8. I could not replicate with gcc.

The link in the original issue points to a compilation error in ../contrib/vr-app/model/burst-sink.h, I was able to find the failure in the clang build in that pipeline

c5847cf9575c7c2c434e290f894ce027f8bbaa2f fixes it for modern clang & is fine for modern gcc. I'll have to check the older compilers and see if this is okay