The `__future__` we relied on is now, where the 3 specific things are
all included [since Python 3.0](https://docs.python.org/3/library/__future__.html):
* absolute_import
* print_function
* unicode_literals
* division
These import statements are no-ops and are no longer necessary.
Add a new action, LoadModuleJobAction, that the driver can use to schedule a
load of a given module before we fan out and invoke the frontend multiple
times. This gives the module interface loader a chance to compile it from a
module interface before we start with parallel invocations, avoiding starting
potentially dozens of redundant compiles of a large module. Start by using this
on the standard library.
Quick fix for rdar://52839445
* E101: indentation contains mixed spaces and tabs
* E111: indentation is not a multiple of four
* E128: continuation line under-indented for visual indent
* E302: expected 2 blank lines, found 1
* W191: indentation contains tabs
- Stronger CHECK lines.
- Don't try to link when there's a fake frontend.
- Give the fake 'ld' an explicit .py suffix, and use a symlink to access it, which
uncovered the first two problems.
This is only the driver side of the work; the frontend doesn't understand
this new -output-filelist option yet. Next commit.
More https://bugs.swift.org/browse/SR-280.
