Fix for BUILD.gn

[Paul Harris]

Please see post here:

https://groups.google.com/g/v8-dev/c/i08BSXO27nk/m/HCwk72MvDgAJ

I notice that v8_heap_base_headers is a header-only target in BUILD.gn,

but it is defined as "v8_source_set()" which ends up as a lib.

It works if you change the line in BUILD.gn:

v8_source_set("v8_heap_base_headers") {

to

v8_header_set("v8_heap_base_headers") {

In this case, this is for MSVC2022.

I guess it works on other platforms as they are able to build an empty .a library file,

but MS's lib.exe doesn't generate .lib files if there are no source inputs.

So then the link call fails as one of the .lib inputs is missing.

cheers,

Paul