ni845x_spi: Add a `ni845x.h` header stub for build tests

The `ni845x_spi' programmer driver depends on a proprietary library,
only available for Windows. As that's not the best circumstances for
build tests, add a header file that provides exactly the definitions
needed to compile the driver.

The compilation result can never be linked. Hence, add another build
target to test compilation of this file only.

Change-Id: I3d291bc16eecb1777062a61362a8eb1548afb7a3
Signed-off-by: Nico Huber <nico.h@gmx.de>
Reviewed-on: https://review.sourcearcade.org/c/flashprog/+/411
diff --git a/util/manibuilder/Makefile b/util/manibuilder/Makefile
index 7109ce2..a9be1fe 100644
--- a/util/manibuilder/Makefile
+++ b/util/manibuilder/Makefile
@@ -4,7 +4,7 @@
 
 CC := ccache cc
 MAKECMD := make
-MAKEARGS := CONFIG_EVERYTHING=yes
+MAKEARGS := CONFIG_EVERYTHING=yes all additional_tests
 MESONCMD := meson
 MESONARGS := -D programmer=all -D classic_cli_print_wiki=enabled --auto-features enabled