LDC lto generate wrong dll export table

[Test123]

The problem is when link with LDC generate lto object, there is 
no export table name.

ldmd2 -mtriple=x86_64-w64-mingw32 -betterC  -flto=full -c ./test.d

```d
import ldc.attributes : assumeUsed;
import core.sys.windows.windows;
@nogc nothrow extern(C):
export int test() @assumeUsed {
         return 0;
}

export extern(Windows) BOOL DllMain(HINSTANCE hInstance, ULONG 
ulReason, LPVOID pvReserved) @assumeUsed {
         return true;
}
```

x86_64-w64-mingw32-clang -flto=full ./test.c -c

```c
#include <windows.h>

BOOL WINAPI DllMain(HINSTANCE hinst,DWORD reason,LPVOID 
lpReserved)
{
	return TRUE;
}

__declspec(dllexport) int test(){
	return 0;
}
```

to link with lld (or use clang -L/dll -shared)

```sh
lld -flavor ld -lmsvcrt -m i386pep --shared -Bdynamic -e 
DllMainCRTStartup --enable-auto-image-base -o test.dll 
mingw/x86_64-w64-mingw32/lib/dllcrt2.o 
mingw/x86_64-w64-mingw32/lib/crtbegin.o 
-Lmingw/x86_64-w64-mingw32/lib -Lmingw/lib 
-Lmingw/x86_64-w64-mingw32/sys-root/mingw/lib 
-Lmingw/lib/clang/14.0.0/lib/windows test.o -ldnsapi -lbcrypt 
-lpsapi -lole32 -liphlpapi -luserenv /dll -lws2_32 
-lssp_nonshared -lmingw32 
mingw/lib/clang/14.0.0/lib/windows/libclang_rt.builtins-x86_64.a 
-lmoldname -lmingwex -ladvapi32 -lshell32 -luser32 -lkernel32 
mingw/x86_64-w64-mingw32/lib/crtend.o -Bdynamic
```


As you can see, c and d code are same, and use same link 
argument. (I replace the test.o with link script to test)

If I build D code without LTO, I get the correct binary like 
clang dose.

Only when I build code with LDC and LTO, the problem exists:

Verify with x86_64-w64-mingw32-objdump --private-headers 
test.dll, you will see random symbol name for LDC & LDC 
bianry(some time empty).