This patch works around a gcc 3.3 bug on AMD64.  On AMD64 the
get_current() function expands to a switch on sizeof which has to be
optimized away by the compiler, finally yielding an inline assembler
statement.  In some cases it seems to get that wrong and forgets to
reference and use the argument.  I have only seen it happen in
binfmt_elf so far.

Work around by just computing "current" once.