[scudo][standalone] Fix -Werror=empty-body error on Fuchsia

[cryptoad]

Summary

Some gcc builders use this, resulting in breakage when the DCHECK is
empty. Add braces.

[vitalybuka]

LGTM even if it's unneeded after D100693

[cryptoad]

https://reviews.llvm.org/D100693 is better.

compiler-rt/lib/scudo/standalone/fuchsia.cpp

void *map(void *Addr, uptr Size, const char *Name, uptr Flags,
   const uint64_t Offset =
       Addr ? reinterpret_cast<uintptr_t>(Addr) - Data->VmarBase : 0;
   if (Offset)
     MapFlags |= ZX_VM_SPECIFIC;
   Status = _zx_vmar_map(Vmar, MapFlags, Offset, Vmo, VmoSize, Size, &P);
   // No need to track the Vmo if we don't intend on resizing it. Close it.
   if (Flags & MAP_RESIZABLE) {
     DCHECK(Data);
-    if (Data->Vmo == ZX_HANDLE_INVALID)
+    if (Data->Vmo == ZX_HANDLE_INVALID) {
       Data->Vmo = Vmo;
-    else
+    } else {
       DCHECK_EQ(Data->Vmo, Vmo);
+    }
   } else {
     CHECK_EQ(_zx_handle_close(Vmo), ZX_OK);
   }
   if (UNLIKELY(Status != ZX_OK)) {
     if (Status != ZX_ERR_NO_MEMORY || !AllowNoMem)
       dieOnMapUnmapError(Status == ZX_ERR_NO_MEMORY);
     return nullptr;
   }