[Bug c++/115686] New: gcc cannot generate weak link function for thread_local variable `TLS init function`

[MacroModel at trajectronix dot onmicrosoft.com via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=115686

            Bug ID: 115686
           Summary: gcc cannot generate weak link function for
                    thread_local variable `TLS init function`
           Product: gcc
           Version: 15.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: MacroModel at trajectronix dot onmicrosoft.com
  Target Milestone: ---

gcc cannot generate weak link function for thread_local variable `TLS init
function`

```cpp

// h1.h

#include <vector>
inline thread_local ::std::vector<int> v{};

// c1.cpp

#include "h1.h"
int main()
{
    v.push_back(1);
}

// c2.cpp

#include "h1.h"
void foo()
{
    v.push_back(2);
}

```

compile:

```bash
g++ -o test c1.cpp c2.cpp -std=c++2c
G:/x86_64-w64-mingw32/bin/../lib/gcc/x86_64-w64-mingw32/15.0.0/../../../../x86_64-w64-mingw32/bin/ld.exe:
C:\Users\User\AppData\Local\Temp\ccQoDAAa.o:c2.cpp:(.text+0x2a): multiple
definition of `TLS init function for v';
C:\Users\User\AppData\Local\Temp\ccjOPJhU.o:c1.cpp:(.text+0x33): first defined
here
```

gcc version:

```bash
Using built-in specs.
COLLECT_GCC=G:\x86_64-w64-mingw32\bin\g++.exe
COLLECT_LTO_WRAPPER=G:/x86_64-w64-mingw32/bin/../libexec/gcc/x86_64-w64-mingw32/15.0.0/lto-wrapper.exe
Target: x86_64-w64-mingw32
Configured with: /home/cqwrteur/toolchains_build/gcc/configure
--with-gxx-libcxx-include-dir=/home/cqwrteur/toolchains/x86_64-w64-mingw32/x86_64-w64-mingw32/include/c++/v1
--prefix=/home/cqwrteur/toolchains/x86_64-w64-mingw32/x86_64-w64-mingw32
--build=x86_64-pc-linux-gnu --host=x86_64-w64-mingw32
--target=x86_64-w64-mingw32 --disable-nls --disable-werror
--enable-languages=c,c++ --enable-multilib --disable-bootstrap
--disable-libstdcxx-verbose --enable-libstdcxx-static-eh-pool
--with-libstdcxx-eh-pool-obj-count=0 --disable-sjlj-exceptions
--enable-libstdcxx-threads --enable-libstdcxx-backtrace
Thread model: win32
Supported LTO compression algorithms: zlib
gcc version 15.0.0 20240622 (experimental) (GCC)
```