tools: Add explicit clean rule for SeaBIOS

Since seabios-dir is cloned during build we need to check that it exists before
recursing into it for clean, following the pattern used for qemu-*-dir etc.

Also remove usage of "buildmakevars2shellvars" except when used to poopulate
the environment for qemu-xen-traditional's xen-setup script, which is the only
user.

Signed-off-by: Ian Campbell <ian.campbell@citrix.com>
Acked-by: Ian Jackson <ian.jackson@eu.citrix.com>
Committed-by: Ian Jackson <ian.jackson@eu.citrix.com>

tools/Makefile

@@ -127,7 +127,6 @@ subdir-all-qemu-xen-traditional-dir subdir-install-qemu-xen-traditional-dir: qem
 
 subdir-clean-qemu-xen-traditional-dir:
 	set -e; if test -d qemu-xen-traditional-dir/.; then \
-		$(buildmakevars2shellvars); \
 		$(MAKE) -C qemu-xen-traditional-dir clean; \
 	fi
 
@@ -162,7 +161,6 @@ subdir-all-qemu-xen-dir subdir-install-qemu-xen-dir: qemu-xen-dir-find
 
 subdir-clean-qemu-xen-dir:
 	set -e; if test -d qemu-xen-dir/.; then \
-		$(buildmakevars2shellvars); \
 		$(MAKE) -C qemu-xen-dir clean; \
 	fi
 

tools/firmware/Makefile

@@ -55,3 +55,8 @@ seabios-dir-force-update:
 		$(GIT) fetch origin; \
 		$(GIT) reset --hard $(SEABIOS_UPSTREAM_TAG); \
 	fi
+
+subdir-clean-seabios-dir:
+	set -e; if test -d seabios-dir/.; then \
+		$(MAKE) -C seabios-dir clean; \
+	fi