Import bmake-20200704

Import bmake-20200704

from ChangeLog:

    (most of this by rillig@)
    o lots of style and white-space cleanup
    o lots more unit tests for variable modifiers
    o simplified description of some functions
    o str.c: refactor Str_Match
    o var.c: debugging output for :@
      constify VarModify parameter
      fix :hash modifier on 16-bit platforms
      remove unnecessary forward declarations
      refactor ApplyModifier_SysV to have less indentation
      simplify code for :E and :R
      clean up code for :H and :T
      refactor ApplyModifiers

    * var.c: we need stdint.h on some platforms to get uint32_t
    * unit-test/Makefile: we need to supress the specific error
    for RE substitution error in modmisc, since it varies accross
    different OS.