latest LLVM will not compile TwoPaCo

[dslarm]

Using LLVM 19.1.0 or ACfL 24.10 (which is built on top of) results in errors compiling due to deleted atomic operator in candidateoccurence.h. The compiler has become more strict on C++ standards.

In particular, we see:

cd /home/rocky/salmon/build_acfl/external/pufferfish/external/twopaco/graphconstructor && armclang++  -I/home/rocky/salmon/external/pufferfish/external/twopaco/graphconstructor -I/home/rocky/salmon/external/install/include -I/home/rocky/salmon/external/pufferfish/external/twopaco/graphconstructor/../common -O3 -DNDEBUG  -fsigned-char -MD -MT external/pufferfish/external/twopaco/graphconstructor/CMakeFiles/twopaco.dir/constructor.cpp.o -MF CMakeFiles/twopaco.dir/constructor.cpp.o.d -o CMakeFiles/twopaco.dir/constructor.cpp.o -c /home/rocky/salmon/external/pufferfish/external/twopaco/graphconstructor/constructor.cpp -std=c++14
In file included from /home/rocky/salmon/external/pufferfish/external/twopaco/graphconstructor/constructor.cpp:22:
In file included from /home/rocky/salmon/external/pufferfish/external/twopaco/graphconstructor/assemblyedgeconstructor.h:4:
In file included from /home/rocky/salmon/external/pufferfish/external/twopaco/graphconstructor/vertexenumerator.h:25:
/home/rocky/salmon/external/pufferfish/external/twopaco/graphconstructor/candidateoccurence.h:61:11: error: overload resolution selected deleted operator '='
   61 |                         count_ = toCopy.count_;
      |                         ~~~~~~ ^ ~~~~~~~~~~~~~
/opt/arm/gcc-14.2.0_RHEL-9/lib/gcc/aarch64-linux-gnu/14.2.0/../../../../include/c++/14.2.0/atomic:904:15: note: candidate function has been explicitly deleted
  904 |       atomic& operator=(const atomic&) = delete;
      |               ^
/opt/arm/gcc-14.2.0_RHEL-9/lib/gcc/aarch64-linux-gnu/14.2.0/../../../../include/c++/14.2.0/atomic:905:15: note: candidate function has been explicitly deleted
  905 |       atomic& operator=(const atomic&) volatile = delete;
      |               ^
/opt/arm/gcc-14.2.0_RHEL-9/lib/gcc/aarch64-linux-gnu/14.2.0/../../../../include/c++/14.2.0/bits/atomic_base.h:354:22: note: candidate function has been explicitly deleted
  354 |       __atomic_base& operator=(const __atomic_base&) = delete;
      |                      ^
/opt/arm/gcc-14.2.0_RHEL-9/lib/gcc/aarch64-linux-gnu/14.2.0/../../../../include/c++/14.2.0/bits/atomic_base.h:355:22: note: candidate function has been explicitly deleted
  355 |       __atomic_base& operator=(const __atomic_base&) volatile = delete;
      |                      ^
/opt/arm/gcc-14.2.0_RHEL-9/lib/gcc/aarch64-linux-gnu/14.2.0/../../../../include/c++/14.2.0/bits/atomic_base.h:367:7: note: candidate function
  367 |       operator=(__int_type __i) noexcept
      |       ^
/opt/arm/gcc-14.2.0_RHEL-9/lib/gcc/aarch64-linux-gnu/14.2.0/../../../../include/c++/14.2.0/bits/atomic_base.h:374:7: note: candidate function
  374 |       operator=(__int_type __i) volatile noexcept
      |       ^
1 error generated.

This can be resolved by changing the right hand side of line 61 to use the load method of toCopy.count_ to get its value instead.