EmulatorPkg: require GCC48 or later

EmulatorPkg: require GCC48 or later

We're about to remove BaseTools support for GCC44..GCC47. Reject those gcc
versions cleanly in "EmulatorPkg/build.sh", and drop build flags too that
are specific to them.

No GCC44..GCC47 references remain under EmulatorPkg after this patch.

Cc: Andrew Fish <afish@apple.com>
Cc: Jordan Justen <jordan.l.justen@intel.com>
Cc: Ruiyu Ni <ruiyu.ni@intel.com>
Ref: https://bugzilla.tianocore.org/show_bug.cgi?id=1377
Contributed-under: TianoCore Contribution Agreement 1.1
Signed-off-by: Laszlo Ersek <lersek@redhat.com>
Reviewed-by: Jordan Justen <jordan.l.justen@intel.com>
Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Reviewed-by: Liming Gao <liming.gao@intel.com>