Minor cleanup in how we run make:
o Move SRCCONF and __MAKE_CONF into the environment to cope with

file paths with spaces in them better.

o Move the rest of the variable setting command line args into

__MAKE_CONF files.

o Trace the commands that we're using to build so they appear at the

top of the log.

o Be more consistent about quoting paths for cd and similar commands

to better cope with paths with spaces in them, though some more
work is likely needed.

o Add some comments about all this.
o Minor formatting tweaks in a couple places

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