Update to 20211221 (#2011469)
    
    * VERSION (_MAKE_VERSION): 20211221
    Merge with NetBSD make, pick up
    o more unit-tests
    o style cleanup
    o in CLEANUP mode, free interned strings at the very end
    o fix memory leak for filenames in .for loops
    o buf.c: avoid memory leak
    o cond.c: condense CondParser_ComparisonOp
    o hash.c: change return type of HashTable_Set to void
    o job.c: change return type of Compat_RunCommand from int to bool
    o main.c: remove bmake_free
    o parse.c: condense repetetive code in ParseDirective
    remove dead code for handling traditional include directives
    clean up parsing of variable assignments
    remove unreachable code for parsing the dependency operator
    clean up loading of files
    fix memory leak in IncludeFile
    o var.c: fix memory leak when parsing a variable name
    fix memory leak from ${.SUFFIXES}
    reduce memory allocation in modifier ':?' and ':C'
    condense RegexReplace for the modifier ':C' and avoid strlen
    merge duplicate code for memory handling in Var_Parse
    distinguish between short-lived and environment variables
    rename VarFreeEnv to VarFreeShortLived