[PATCH] libxl: avoid golang building without CONFIG_GOLANG=y

[Jan Beulich <jbeulich@xxxxxxxx>]

While this doesn't address the real problem I've run into (attempting to
update r/o source files), not recursing into tools/golang/xenlight/ is
enough to fix the build for me for the moment. I don't currently see why
60db5da62ac0 ("libxl: Generate golang bindings in libxl Makefile") found
it necessary to invoke this build step unconditionally.

Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
---
I'm also having trouble to see why, besides the idl-gen target in
tools/golang/xenlight/Makefile, the commit also adds such a target to
(and mentions it in [only] a comment in) tools/libxl/Makefile.

--- a/tools/libxl/Makefile
+++ b/tools/libxl/Makefile
@@ -282,7 +282,9 @@ _libxl_type%.h _libxl_type%_json.h _libx
 # about races with tools/golang/xenlight/Makefile:all
 .PHONY: idl-external
 idl-external:
+ifeq ($(CONFIG_GOLANG),y)
        $(MAKE) -C $(XEN_ROOT)/tools/golang/xenlight idl-gen
+endif
 
 LIBXL_IDLGEN_FILES = _libxl_types.h _libxl_types_json.h _libxl_types_private.h 
_libxl_types.c \
        _libxl_types_internal.h _libxl_types_internal_json.h 
_libxl_types_internal_private.h _libxl_types_internal.c