If your PostgreSQL server was built using MinGW-w64 (which you can
check by running pg_config and looking for mingw), then you can build
PL/Java using the same toolchain. PL/Java has been successfully built
on Windows using MinGW-w64 and MSYS2, with a 64-bit PostgreSQL build
and a 64-bit Java development kit (JDK).
MSYS2 can be installed using its “one-click installer” (which, by one way of counting, takes closer to six clicks).
If you are building on Windows (that is, not using some other platform
to cross-compile for Windows), then installation of any other software
prerequisites mentioned in the build instructions should be
done from within an MSYS2 Shell, which can be found under the MSYS2
entry on the Start menu.
For example, the 64-bit compiler toolchain can be installed with the command
pacman -S mingw-w64-x86_64-gcc
Other prerequisites can be installed similarly. You should make sure that all of the test commands shown for the software prerequisites in the build instructions succeed, and the versions they report are the versions that you intend to use.
The Maven commands for building PL/Java should be run within the
MinGW-w64 shell, which should be available under the MSYS2 entry
on the Start menu after the toolchain has been installed.
The PL/Java build detects this environment by seeing the environment
variable MSYSTEM with the value MINGW64.
These may be possible, but have not been tested. If there is a need to build PL/Java with a 32-bit PostgreSQL and 32-bit JDK, please open an issue.
More information on installing MSYS2 and MinGW-w64 can be found in
a helpful StackOverflow answer.