ArmPkg/CompilerIntrinsicsLib ARM: make memset() weak again

ArmPkg/CompilerIntrinsicsLib ARM: make memset() weak again

After the recent update of CompilerIntrinsicsLib, our memset() is no
longer emitted as a weak symbol. On ARM, this may cause problems when
combining this library with another library that supplies memset() [e.g.,
CryptoPkg/IntrinsicLib], due to the fact that the object also supplies
the __aeabi_memXXX entry points, which can only be satisfied by this
object. So make our memset() weak again, to let the other implementation
take precedence.

Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Reviewed-by: Leif Lindholm <leif.lindholm@linaro.org>