Make supports specifying all types of variables on the command line
(using =, :=, +=, and other variable references. When running soong_ui
through make/makeparallel these all effectively become environment
variables.
So in preparation to remove the Make wrapper, support a simplified form
of this syntax, roughly equivalent to what the shell supports if
specified before the command (<NAME>=<VALUE>).
Test: m -j blueprint_tools
Change-Id: I08fa2b86710f282e619b0cc324a3e5bbaf62d26e
In preparation to remove Make/makeparallel from soong_ui startup, we
need to preserve compatibility with the different ways that make
supports the -j option.
Nothing changes unless Make/makeparallel is removed from the startup.
Once that is removed, not specifying a -j value will be equivalent to
'-j' instead of '-j1', like Ninja. A value will also be supported when
specifying -k, like Ninja (though specifying it alone will be equivalent
to '-k 0').
Test: m -j blueprint_tools
Change-Id: I9d5d59bedd4f6e5cca76bdb4cd47e0b5b7d523f0
