support/kconfig/merge_config.sh: avoid false positive matches from comment lines

support/kconfig/merge_config.sh: avoid false positive matches from comment lines

We are using empty CONFIG_PREFIX_. This results in false positive match
for comment lines when merging config fragments.

To avoid false positive reports, we use separate sed expressions and
address comment lines explicitly.

This is actually is in the Linux kernel mainline (v4.20-rc2):
6bbe4385d035c6fac56f840a59861a0310ce137b
("kconfig: merge_config: avoid false positive matches from comment lines")

Signed-off-by: Nasser Afshin <Afshin.Nasser@gmail.com>
Reviewed-by: Petr Vorel <petr.vorel@gmail.com>
Acked-by: "Yann E. MORIN" <yann.morin.1998@free.fr>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>