Align Kconfig and Kbuild logic to Linux 4.18 release with minimal impact
on files outside of this scope.

Our previous Kconfig sync was done by commit e91610da ("kconfig:
re-sync with Linux 4.17-rc4").

A very small number of changes upstream since our sync with v4.17-rc4
that exist in the v4.18 release have already been applied here and have
been omitted from the list in this commit (and are readily available in
our own git history).

The imported Linux commits are:
[From prior to v4.17-rc4]
39a33ff80a25 kbuild: remove cc-option-align
db547ef19064 Kbuild: don't add obj tree in additional includes
b999596b963a Kbuild: don't add ../../ to include path

[From v4.17 to v4.18]
b3aa58d2e85d fixdep: suppress consecutive / from file paths in dependency list files
74656b682902 kbuild: disable new dtc graph and unit-address warnings
74d931716151 genksyms: remove symbol prefix support
e6ecfb45072c kbuild: do not display CHK for filechk
0b669a5076fd kconfig: refactor Qt ...