rust: enable debuginfo

This gets split out in do_package, so there's no harm in including it.
It is useful to be able to get debug info for the standard library by
installing the -dbg package.

recipes/rust/rust.inc

@@ -306,6 +306,7 @@ do_configure () {
 		"--disable-docs"			\
 		"--disable-manage-submodules"           \
 		"--disable-debug"			\
+		"--enable-debuginfo"			\
 		"--enable-optimize"			\
 		"--enable-optimize-cxx"			\
 		"--enable-optimize-llvm"		\