Makefile: CC_IMPLICIT_FALLTHROUGH passed quoted as argument to gcc

[Salvatore Bonaccorso]

Hi Gustavo,

Since dee2b702bcf0 ("kconfig: Add support for -Wimplicit-fallthrough")
CONFIG_CC_IMPLICIT_FALLTHROUGH value is passed quoted to the gcc
invocation.

This appears to cause issues for (external) module builds. It was
reported in Debian for the nvidia module, cf.
https://bugs.debian.org/1001083 but might happen as well in other
cases.

Andreas suggested to replace the

KBUILD_CFLAGS += $(KBUILD_CFLAGS-y) $(CONFIG_CC_IMPLICIT_FALLTHROUGH)

with

KBUILD_CFLAGS += $(KBUILD_CFLAGS-y) $(patsubst "%",%,$(CONFIG_CC_IMPLICIT_FALLTHROUGH))

Is this something you would consider doing or should the issue be
handled exclusively in the particular OOT module build case?

Regards,
Salvatore