To avoid double loops, a couple now use fileinput module.

CC and CXX tests switch to using general mylink.py fixture instead of
locally defined linker script.  This did mean that the marker for the
mock linker that the script removes had to be harmonized as #link - some
were using /*link*/.

Could not switch CC/CXX to use the general mycompile.py mock compiler
due to difference in intent: mycompile.py is intended to plug in as a
*COM variable, which means the whole cmdline is in the caller's control.
mycc.py is intended to plug in as CC and mycxx.py as CXX, which means
standard os-dependent construction vars will be passed via the default
CCCOM and CXXCOM and have to be handled.

Signed-off-by: Mats Wichmann <mats@linux.com>

Eliminate unneeded imports, and a few unneeded statements -
usually "pass" where it is not syntactically needed.

A couple of import try blocks were eliminated or changed
when they're "cannot happen" due to current floor Python version.

Signed-off-by: Mats Wichmann <mats@linux.com>

Various tests called subdir several times with the same directory,
which is pointless.  In previous code, this emitted a message
though it did not fail.  Stop doing that.

The dir_fixture() method did some convoluted things to make sure
the directories to write to exist, change this around to simplify.
The subdir() method already combines the testdir, so dir_fixture
doesn't need to.  Also handle more cleanly the case of the target
directory being an absolute path, which seems to have been intended,
but would not work.

Also clean up file_fixture() along the same principles.

Change the subdir() method to not need to be given an ordered
list of directories; instead call os.makedirs on each so
intermediate steps are made automatically.  Along the way,
the print about making a directory that already existed vanishes.

Tests which did os.path.join on directory pieces when calling
file_fixture no longer do so, since file_fixture (and dir_fixture)
do joining on an arg which is a list of paths like many other scons
functions.

The testing doc was updated to fix some wording and reflect
the above changes.

Signed-off-by: Mats Wichmann <mats@linux.com>

This converts the remaining tests that called os.system
themselves to use subprocess instead.

Signed-off-by: Mats Wichmann <mats@linux.com>

File closes in msvs tool
Context manager in rpm tool
Dummy compiler, assembler scripts can be called in unexpected
  ways (namely by gcc tool init), which passes --version flag.
  don't take exception on the getopt call.
Try again to undo my breakage of _subproc, which was failing on Win+PY27

Signed-off-by: Mats Wichmann <mats@linux.com>

On a linux host (missing some things that may be on the Travis CI
setup), Py3.8a3 now shows 19 fails, 1048 pass, with 84 Warning: messages.

Signed-off-by: Mats Wichmann <mats@linux.com>