BaseTools: use unsigned chars on ARM architectures
BaseTools: use unsigned chars on ARM architectures

By default, the ARM architectures have unsigned chars, whereas the other
architectures supported by EDK2 by default have signed chars.
However, EDK2 uses -funsigned-chars on those architectures to change the
default behaviour.

Unfortunately, the ARM architectures explicitly break their default
behaviour by specifying -fsigned-chars (I presume in a pre-emptive
attempt at avoiding incompatibility).

Since this situation is already confusing enough, switch the ARM
architectures to also specify -funsigned-chars explicitly rather than
just dropping the current parameter.

Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Leif Lindholm <a613079f0455438b29e28a9c5b9eb3779a81a33a@linaro.org>
Reviewed-by: Ard Biesheuvel <66d3c5fdaeea7ff1f996ad04f2c45e08ab38e2f5@linaro.org>
Reviewed-by: Liming Gao <6480311aeeb4b006862f6d13ebabddc03f51e507@intel.com>

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