perf arm64: Simplify mksyscalltbl

This patch isn't intended to have any effect on the compiled code.  It
just removes one level of indirection: calling the *host* compiler to
build and then run a program that just printf:s the numerical entries of
the syscall-table.  In other words, the generated syscalls.c changes
from:

	[46] = "ftruncate",
to:
	[__NR3264_ftruncate] = "ftruncate",

The latter is as good as the former to the user of perf, and this can be
done directly by the shell-script.  The syscalls defined as non-literal
values (like "#define __NR_ftruncate __NR3264_ftruncate") are trivially
resolved at compile-time without namespace-leaking and/or collision for
its sole user, perf/util/syscalltbl.c, that just #includes the generated
file.  A future "-mabi=32" support would probably have to handle this
differently, but that is a pre-existing problem not affected by this
simplification.

Calling the *host* compiler only complicates things and accidentally can
get a completely wrong set of files and syscall numbers, see earlier
commits.  Note that the script parameter hostcc is now unused.

At the time of this patch, powerpc (the origin, see comments), and also
e.g. x86 has moved on, from filtering "gcc -dM -E" output to reading
separate specific text-file, a table of syscall numbers.  IMHO should
arm64 consider adopting this.

Signed-off-by: Hans-Peter Nilsson <hp@axis.com>

Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Reviewed-by: Leo Yan <leo.yan@linaro.org>
Tested-by: Leo Yan <leo.yan@linaro.org>
Acked-by: Arnd Bergmann <arnd@arndb.de>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: John Garry <john.garry@huawei.com>
Cc: Kim Phillips <kim.phillips@arm.com>
Cc: Leo Yan <leo.yan@linaro.org>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Mathieu Poirier <mathieu.poirier@linaro.org>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Will Deacon <will@kernel.org>
Cc: linux-arm-kernel@lists.infradead.org
Link: https://lore.kernel.org/r/20201228024159.2BB66203B5@pchp3.se.axis.com


Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>