BaseTools/tools_def ARM: emit PIC veneers

BaseTools/tools_def ARM: emit PIC veneers

The ARM linker may emit veneers, i.e., trampolines, when ordinary
direct relative branches cannot be used, e.g., for Thumb interworking
or branch targets that are out of range.

Usually, such veneers carry an absolute reference to the branch
target, which is problematic for us, since these absolute references
are not covered by annotations that are visible to GenFw in the
PE/COFF conversion, and so these absolute references are not fixed
up by the PE/COFF loader at runtime.

So switch to all ARM GNU ld toolchains to position independent veneers.

Contributed-under: TianoCore Contribution Agreement 1.1
Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>