kbuild: modinst: Fix build error when CONFIG_MODULE_SIG_KEY is a PKCS#11 URI

When CONFIG_MODULE_SIG_KEY is PKCS#11 URI (pkcs11:*), signing of modules
fails:

scripts/sign-file sha256 /.../linux/pkcs11:token=foo;object=bar;pin-value=1111 certs/signing_key.x509 /.../kernel/crypto/tcrypt.ko
Usage: scripts/sign-file [-dp] <hash algo> <key> <x509> <module> [<dest>]
scripts/sign-file -s <raw sig> <hash algo> <x509> <module> [<dest>]

First, we need to avoid adding the $(srctree)/ prefix to the URL.

Second, since the kconfig string values no longer include quotes, we need to add
them again when passing a PKCS#11 URI to sign-file. This avoids
splitting by the shell if the URI contains semicolons.

Fixes: 4db9c2e3d055 ("kbuild: stop using config_filename in scripts/Makefile.modsign")
Fixes: 129ab0d2d9f3 ("kbuild: do not quote string values in include/config/auto.conf")
Signed-off-by: Jan Luebbe <[e-mail]>
Signed-off-by: Masahiro Yamada <[e-mail]>

scripts/Makefile.modinst

···
 # Don't stop modules_install even if we can't sign external modules.
 #
 ifeq ($(CONFIG_MODULE_SIG_ALL),y)
+ifeq ($(filter pkcs11:%, $(CONFIG_MODULE_SIG_KEY)),)
 sig-key := $(if $(wildcard $(CONFIG_MODULE_SIG_KEY)),,$(srctree)/)$(CONFIG_MODULE_SIG_KEY)
+else
+sig-key := $(CONFIG_MODULE_SIG_KEY)
+endif
 quiet_cmd_sign = SIGN    $@
-      cmd_sign = scripts/sign-file $(CONFIG_MODULE_SIG_HASH) $(sig-key) certs/signing_key.x509 $@ \
+      cmd_sign = scripts/sign-file $(CONFIG_MODULE_SIG_HASH) "$(sig-key)" certs/signing_key.x509 $@ \
                  $(if $(KBUILD_EXTMOD),|| true)
 else
 quiet_cmd_sign :=