kbuild: add CONFIG_VMLINUX_MAP expert option

It can be quite useful to have ld emit a link map file, in order to
debug or verify that special sections end up where they are supposed
to, and to see what LD_DEAD_CODE_DATA_ELIMINATION manages to get rid
of.

The only reason I'm not just adding this unconditionally is that the
.map file can be rather large (several MB), and that's a waste of
space when one isn't interested in these things. Also make it depend
on CONFIG_EXPERT.

Signed-off-by: Rasmus Villemoes <linux@rasmusvillemoes.dk>
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
diff --git a/.gitignore b/.gitignore
index 3af6627..3adea59 100644
--- a/.gitignore
+++ b/.gitignore
@@ -59,6 +59,7 @@
 /linux
 /vmlinux
 /vmlinux.32
+/vmlinux.map
 /vmlinux.symvers
 /vmlinux-gdb.py
 /vmlinuz