buildman: Always use the full path in CROSS_COMPILE

The feature to set the toolchain path does not seem to be needed. It
causes problems with venv (see [1]). Let's remove it.

Add some tests while we are here.

It does not look like any docs changes are needed for this.

[1] https://patchwork.ozlabs.org/project/uboot/patch/20240621131423.2363294-6-sjg@chromium.org/

Signed-off-by: Simon Glass <sjg@chromium.org>
Suggested-by: Tom Rini <trini@konsulko.com>
Reviewed-by: Tom Rini <trini@konsulko.com>
Reviewed-by: Andrejs Cainikovs <andrejs.cainikovs@toradex.com>
diff --git a/tools/buildman/control.py b/tools/buildman/control.py
index 464835c..037854d 100644
--- a/tools/buildman/control.py
+++ b/tools/buildman/control.py
@@ -788,10 +788,8 @@
     builder = Builder(toolchains, output_dir, git_dir,
             args.threads, args.jobs, checkout=True,
             show_unknown=args.show_unknown, step=args.step,
-            no_subdirs=args.no_subdirs, full_path=args.full_path,
-            verbose_build=args.verbose_build,
-            mrproper=args.mrproper,
-            fallback_mrproper=args.fallback_mrproper,
+            no_subdirs=args.no_subdirs, verbose_build=args.verbose_build,
+            mrproper=args.mrproper, fallback_mrproper=args.fallback_mrproper,
             per_board_out_dir=args.per_board_out_dir,
             config_only=args.config_only,
             squash_config_y=not args.preserve_config_y,