BaseTool/tools_def GCC5: enable optimization for ARM/AARCH64 DEBUG builds

BaseTool/tools_def GCC5: enable optimization for ARM/AARCH64 DEBUG builds

Enable optimization for DEBUG builds, to make it more usable in terms of
performance, and to give more coverage to the LTO builds. Also, some
diagnostics are only enabled when optimization is enabled.
NOOPT builds can now also be created, which will retain the behavior DEBUG
builds had previously.

Note that this aligns ARM and AARCH64 with the x86 architectures, which
already use optimization for DEBUG builds.

In order to preserve existing behavior for users of older toolchains,
keep GCC49 and older as-is.

Contributed-under: TianoCore Contribution Agreement 1.1
Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Acked-by: Laszlo Ersek <lersek@redhat.com>
Tested-by: Leif Lindholm <leif.lindholm@linaro.org>
Reviewed-by: Leif Lindholm <leif.lindholm@linaro.org>
Reviewed-by: Liming Gao <liming.gao@intel.com>