gcc: Don't mess with test-suite exclusion

gcc: Don't mess with test-suite exclusion

We used to exclude GCC's test-suite for quite some time now
mostly for the sake of space reduction.

But:
 1. On each GCC version bump we need to revise that functionality
    as we need to accommodate changes in GCC sources and this
    couldn't be automated

 2. The space reduction is significant, but not huge. The two test
    suites together take up 290MB, out of 660MB total for GCC (each of
    them times two because there is the -initial and -final copy).
    However, whenever we build GCC, we also have kernel headers (about
    900MB) and a libc (e.g. glibc is 250MB). So at best, it saves less
    than 20%.

 3. It doesn't really save on build time either.
    Below are timings of 2 runs on my laptop:

    a) Vanilla master:
    --------------------->8---------------------
    time make host-gcc-final
    real	7m15.114s
    user	19m36.611s
    sys 	2m26.927s
    --------------------->8---------------------

    b) master + testsuite:
    --------------------->8---------------------
    time make host-gcc-final
    real	7m59.860s
    user	20m21.668s
    sys 	2m36.618s
    --------------------->8---------------------

    From figures above it's seen that difference is ~45 seconds
    or ~10%. On both host-gcc-initial and -final we may save ~1.5
    minutes... but these are not the only components we build and
    compared to a total toolchain build time IMHO it is not that
    much time to care especially traded for maintenance costs
    on GCC version bumps.

Signed-off-by: Alexey Brodkin <abrodkin@synopsys.com>
Cc: Thomas Petazzoni <thomas.petazzoni@bootlin.com>
Cc: Bernd Kuhls <bernd.kuhls@t-online.de>
Cc: Romain Naour <romain.naour@gmail.com>
Cc: Peter Korsgaard <peter@korsgaard.com>
Cc: Arnout Vandecappelle <arnout@mind.be>
[Arnout: add explanation about size impact.]
Signed-off-by: Arnout Vandecappelle (Essensium/Mind) <arnout@mind.be>