[scudo][Fuchsia] Don't assume MapPlatformData::Vmar is valid

[abrachet]

Summary

After https://reviews.llvm.org/D129237, the assumption that any non-null data contains a valid vmar handle is no longer true. Generally this code here needs cleanup, but in the meantime this fixes errors on Fuchsia.

[mcgrathr]

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

60

It's better not to call the function unconditionally, especially since it's a PLT jump.
You can use = (Data && Data->Vmar != ZX_HANDLE_INVALID) ? Data->Vmar : _zx_vmar_root_self(); instead.

[ddcc]

I'm not familiar with fuchsia and aren't using its scudo bindings

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

void *map(void *Addr, uptr Size, const char *Name, uptr Flags,
           MapPlatformData *Data) {
   DCHECK_EQ(Size % getPageSizeCached(), 0);
   const bool AllowNoMem = !!(Flags & MAP_ALLOWNOMEM);
 
   // For MAP_NOACCESS, just allocate a Vmar and return.
   if (Flags & MAP_NOACCESS)
     return allocateVmar(Size, Data, AllowNoMem);
 
-  const zx_handle_t Vmar = Data ? Data->Vmar : _zx_vmar_root_self();
-  CHECK_NE(Vmar, ZX_HANDLE_INVALID);
+  zx_handle_t Vmar = _zx_vmar_root_self();
+  if (Data && Data->Vmar != ZX_HANDLE_INVALID)
+    Vmar = Data->Vmar;
 
   zx_status_t Status;
   zx_handle_t Vmo;
   uint64_t VmoSize = 0;
   if (Data && Data->Vmo != ZX_HANDLE_INVALID) {
     // If a Vmo was specified, it's a resize operation.
     CHECK(Addr);
     DCHECK(Flags & MAP_RESIZABLE);
void unmap(void *Addr, uptr Size, uptr Flags, MapPlatformData *Data) {
   if (Flags & UNMAP_ALL) {
     DCHECK_NE(Data, nullptr);
     const zx_handle_t Vmar = Data->Vmar;
     DCHECK_NE(Vmar, _zx_vmar_root_self());
     // Destroying the vmar effectively unmaps the whole mapping.
     CHECK_EQ(_zx_vmar_destroy(Vmar), ZX_OK);
     CHECK_EQ(_zx_handle_close(Vmar), ZX_OK);
   } else {
-    const zx_handle_t Vmar = Data ? Data->Vmar : _zx_vmar_root_self();
+    zx_handle_t Vmar = _zx_vmar_root_self();
+    if (Data && Data->Vmar != ZX_HANDLE_INVALID)
+      Vmar = Data->Vmar;
     const zx_status_t Status =
         _zx_vmar_unmap(Vmar, reinterpret_cast<uintptr_t>(Addr), Size);
     if (UNLIKELY(Status != ZX_OK))
       dieOnMapUnmapError();
   }
   if (Data) {
     if (Data->Vmo != ZX_HANDLE_INVALID)
       CHECK_EQ(_zx_handle_close(Data->Vmo), ZX_OK);