Kconfig updates for v4.21 - support -y option for merge_config.sh to avoid downgrading =y to =m - remove S_OTHER symbol type, and touch include/config/*.h files correctly - fix file name and line number in lexer warnings - fix memory leak when EOF is encountered in quotation - resolve all shift/reduce conflicts of the parser - warn no new line at end of file - make 'source' statement more strict to take only string literal - rewrite the lexer and remove the keyword lookup table - convert to SPDX License Identifier - compile C files independently instead of including them from zconf.y - fix various warnings of gconfig - misc cleanups