meson: don't build test programs by default

They are only used when running tests, and are included as depedencies
of the test cases themselves already. Marking them to not build by
default, means that 291 compile edges can be skipped when only running

```
meson setup builddir/
ninja -C builddir/
meson install -C builddir/
```

resulting in an overall much faster build. Instead they will be compiled
on-demand by `meson test`, only for users that actually run the tests.

Signed-off-by: Eli Schwartz <[email protected]>
Message-ID: <[email protected]>
Signed-off-by: David Gibson <[email protected]>

tests/meson.build

@@ -1,7 +1,9 @@
 trees = static_library('trees', files('trees.S'), c_args: '-D__ASSEMBLY__',
+                       build_by_default: false,
                        include_directories: libfdt_inc)
 
 dumptrees = executable('dumptrees', files('dumptrees.c'),
+                       build_by_default: false,
                        link_with: trees, dependencies: libfdt_dep)
 
 dumptrees_dtb = custom_target(
@@ -111,7 +113,7 @@ endif
 
 tests_exe = []
 foreach t: tests
-  tests_exe += executable(t, files(t + '.c'), dependencies: test_deps, link_args: extra_link_args)
+  tests_exe += executable(t, files(t + '.c'), dependencies: test_deps, link_args: extra_link_args, build_by_default: false)
 endforeach
 
 run_tests = find_program('run_tests.sh')