plugins: add dllexport and dllimport to api funcs

plugins: add dllexport and dllimport to api funcs

In qemu-plugin.h, mark all API functions as __declspec(dllexport) when
compiling the executables, and as __declspec(dllimport) when being used
to compile plugins against.

Signed-off-by: Greg Manning <gmanning@rapitasystems.com>
Reviewed-by: Alex Bennée <alex.bennee@linaro.org>
Message-Id: <20231102172053.17692-2-gmanning@rapitasystems.com>
Reviewed-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Message-Id: <20231106185112.2755262-14-alex.bennee@linaro.org>