perf tools: Allow to specify custom linker command

perf tools: Allow to specify custom linker command

Allow to specify custom linker command. This fixes MIPS64 builds for
64-bit userspace as it will allow to pass a linker using the correct
linker flags for 64-bit ABI (by default GNU binutils ld will assume
N32).

Signed-off-by: Aaro Koskinen <[email protected]>
Acked-by: Jiri Olsa <[email protected]>
Cc: Paul Mackerras <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Link: http://lkml.kernel.org/r/[email protected]
Signed-off-by: Arnaldo Carvalho de Melo <[email protected]>