kbuild: Fix permissions of modules.builtin.modinfo

Currently, modules.builtin.modinfo is created with executable permissions
(0755). This is because after commit 39cfd5b ("kbuild: extract
modules.builtin.modinfo from vmlinux.unstripped"), modules.builtin.modinfo
is extracted from vmlinux.unstripped using objcopy. When extracting
sections, objcopy inherits attributes from the source ELF file.

Since modules.builtin.modinfo is a data file and not an executable,
it should have regular file permissions (0644). The executable bit
can trigger warnings in Debian's Lintian tool.

Explicitly remove the executable bit after generation.

Fixes: 39cfd5b ("kbuild: extract modules.builtin.modinfo from vmlinux.unstripped")
Signed-off-by: Ethan Zuo <yuxuan.zuo@outlook.com>
Link: https://patch.msgid.link/SY0P300MB0609F6916B24ADF65502940B9C91A@SY0P300MB0609.AUSP300.PROD.OUTLOOK.COM
Signed-off-by: Nicolas Schier <nsc@kernel.org>

Author: YuxuanZuo

scripts/Makefile.vmlinux

@@ -113,7 +113,8 @@ vmlinux: vmlinux.unstripped FORCE
 # what kmod expects to parse.
 quiet_cmd_modules_builtin_modinfo = GEN     $@
       cmd_modules_builtin_modinfo = $(cmd_objcopy); \
-                                    sed -i 's/\x00\+$$/\x00/g' $@
+                                    sed -i 's/\x00\+$$/\x00/g' $@; \
+                                    chmod -x $@
 
 OBJCOPYFLAGS_modules.builtin.modinfo := -j .modinfo -O binary