[libunwind] Silence warnings about unused variables. NFC.

[mstorsjo]

Summary

This variable was considered unused if building with log messages
disabled, when building for Windows with Dwarf exception handling
(i.e. for i386).

[MaskRay]

Looks great!

if building with log messages disabled

Perhaps specify the preciser condition: when NDEBUG is defined

libunwind/src/AddressSpace.hpp

#elif defined(_LIBUNWIND_SUPPORT_DWARF_UNWIND) && defined(_WIN32)
   HMODULE mods[1024];
   HANDLE process = GetCurrentProcess();
   DWORD needed;
 
   if (!EnumProcessModules(process, mods, sizeof(mods), &needed)) {
     DWORD err = GetLastError();
     _LIBUNWIND_TRACE_UNWINDING("findUnwindSections: EnumProcessModules failed, "
                                "returned error %d", (int)err);
+    (void)err;
     return false;
   }
 
   for (unsigned i = 0; i < (needed / sizeof(HMODULE)); i++) {
     PIMAGE_DOS_HEADER pidh = (PIMAGE_DOS_HEADER)mods[i];
     PIMAGE_NT_HEADERS pinh = (PIMAGE_NT_HEADERS)((BYTE *)pidh + pidh->e_lfanew);
     PIMAGE_FILE_HEADER pifh = (PIMAGE_FILE_HEADER)&pinh->FileHeader;
     PIMAGE_SECTION_HEADER pish = IMAGE_FIRST_SECTION(pinh);