Kconfig updates for v4.19

- show clearer error messages where pkg-config is needed, but not
  installed

- rename SYMBOL_AUTO to SYMBOL_NO_WRITE to reflect its semantics

- create all necessary directories by Kconfig tool itself instead
  of Makefile

- update the .config unconditionally when syncconfig is invoked

- use 'include' directive instead of '-include' where
  include/config/{auto,tristate}.conf is mandatory

- do not try to update the .config when running install targets

- add .DELETE_ON_ERROR to delete partially updated files

- misc cleanups and fixes
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