kbuild: enable -Wcast-function-type-strict unconditionally

All known function cast warnings are now addressed, so the warning can be
enabled globally to catch new ones more quickly.

Link: https://lkml.kernel.org/r/[e-mail]
Signed-off-by: Arnd Bergmann <[e-mail]>
Reviewed-by: Kees Cook <[e-mail]>
Cc: Masahiro Yamada <[e-mail]>
Cc: Nathan Chancellor <[e-mail]>
Cc: Nicolas Schier <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>

scripts/Makefile.extrawarn

···
 KBUILD_CFLAGS += $(call cc-disable-warning, pointer-to-enum-cast)
 KBUILD_CFLAGS += -Wno-tautological-constant-out-of-range-compare
 KBUILD_CFLAGS += $(call cc-disable-warning, unaligned-access)
-KBUILD_CFLAGS += $(call cc-disable-warning, cast-function-type-strict)
 KBUILD_CFLAGS += -Wno-enum-compare-conditional
 KBUILD_CFLAGS += -Wno-enum-enum-conversion
 endif