kconfig: silence warning when parsing auto.conf when a symbol has changed type
kconfig: silence warning when parsing auto.conf when a symbol has changed type

When a symbol changes type from tristate to bool, and was previously set to
'm', a subsequent silentoldconfig would warn about inconsistency, such as:

    include/config/auto.conf:3014:warning: symbol value 'm' invalid for
    HOTPLUG_PCI_PCIE

Seen by Linus with the merge in aa8032b (sequence to reproduce by Michal):
    git checkout 1fe0135
    make mrproper
    make allmodconfig
    make silentoldconfig
    git checkout aa8032b
    make allmodconfig
    make silentoldconfig

Since HOTPLUG_PCI_PCIE changed from tristate to bool in aa8032b, it was
previously set to 'm' in auto.conf by the first allmodconfig+silentoldconfig,
but then was set to 'y' by the second allmodconfig. Then the second
silentoldconfig prints the warning.

The warning in this case is a spurious warning, which happens at the time
kconfig tries to detect symbols that have changed, to touch the empty
header files in include/config used for dependency-tracking by make.

Silence the warning when we read the old auto.conf file, since it is
perfectly legit that a symbol changed type since the previous call.

Thread in:
    http://marc.info/?l=linux-pci&m=137569198904000&w=2

Reported-by: Linus Torvalds <69652caca27c8b940640ad396ab71f93cacec34f@linux-foundation.org>
Signed-off-by: "Yann E. MORIN" <b375a36861a21dce61868a5a9b415811d17b4e97@free.fr>
Cc: Linus Torvalds <69652caca27c8b940640ad396ab71f93cacec34f@linux-foundation.org>
Cc: Michal Marek <0c835876a532a476f30fdb1f6e963bae6c5a1a04@suse.cz>
Cc: Thomas Petazzoni <a5d87d2bd7c424ee5cbdb4e978635bf653d5a005@free-electrons.com>
Cc: Bjorn Helgaas <f10ec01be0c6b54271af5c550cd257810bdf3268@google.com>
Cc: Yinghai Lu <0674548f4d596393408a51d6287a76ebba2f42aa@kernel.org>
Cc: Benjamin Herrenschmidt <a7089bb6e7e92505d88aaff006cbdd60cc9120b6@kernel.crashing.org>

KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs