tests: run_make: options to do command redirection

tests: run_make: options to do command redirection

Let's improve the API of the 'run_make()' helper shell function by
adding three new options:

  -O   Save the standard output from make on disk, in a regular file
       named 'stdout'.

  -E   Save the standard error from make on disk, in a regular file
       named 'stderr'.

  -M   Save both the standard output and standard error from make on
       disk, in a regular file named 'output'. This option supersedes
       both the '-O' and '-E' options.

This new API has two main advantages.

  1. Its use will allow us to get rid of more cumbersome idioms
     like, e.g.,

       $MAKE check >stdout && { cat stdout; exit 1; }
       cat stdout

     That can now be substituted with a simpler one:

       run_make -e FAIL -O check

  2. More importantly, using the new API we will prevent any extra output
     from the shell traces of the code in run_make to be redirected along
     with the make stderr (where that was redirected).  This problem was
     present in usages like, e.g.,

       run_make TESTS=foo.test check 2>stderr && exit 1
       grep 'expected error message' stderr

     Such usages are now to be rewritten as follows:

       run_make -e FAIL -E TESTS=foo.test check
       grep 'expected error message' stderr

     ensuring that 'stderr' won't end up containing unrelated stuff.

Note that we do not convert in bulk the old idioms and the use of
redirected 'run_make' invocations with this patch.  We only convert
some occurrences, to ensure that the new implementation of 'run_make'
is sound enough.  More sweeping conversions will likely be done in
follow-up patches.

* t/ax/am-test-lib.sh (run_make): Enhance and implement the extended API.
* t/tap-xfail-tests.sh: Use the new 'run_make' API.
* t/test-driver-cond.sh: Likewise.
* t/tests-environment-fd-redirect.sh: Likewise.
* t/uninstall-fail.sh: Likewise.
* t/yacc-dist-nobuild.sh: Likewise.

Signed-off-by: Stefano Lattarini <stefano.lattarini@gmail.com>