Where is libpq_fe.h

The following documentation comment has been logged on the website:

Page: https://www.postgresql.org/docs/12/libpq.html
Description:

When building an app or library that links with libpq.dll it is obviously
necessary to include libpq_fe.h. The documentation recommends using binary
distributions of PostgreSQL (otherwise I would build from source) but it
seems version 12 installer (windows) includes the lib file but not the
headers. The documentation does not explain where to obtain the header
files. Earlier installer versions included the required header files. It is
unclear from the documentation where to find this information. This leads to
wasted time by developers such as myself. Now since I'm building both 32 and
64 bit I'll now be using version 12 libpq for 64 bit apps and version 10 for
32 bit because versions 11 12 have dropped 32 bit support. I could, of
course, be lazy and use the header for version 10 and the lib for version 12
when building my 64 bit interface. There would be strong a likelihood that
this could create something with a hideous binary incompatibility.
Alternatively I could download the source and hope that the headers actually
match the binary version as this would be more likely to succeed. I see
mention elsewhere of use of sudo apt get and suchlike for linux but not in
your docs anywhere at least not searchable.