perf LoongArch: Simplify mksyscalltbl

In order to print the numerical entries of the syscall table,
there is no need to call the host compiler to build and then
run a program, this can be done directly by the shell script.

This is similar with commit 9854e7ad ("perf arm64: Simplify
mksyscalltbl"). For now, the mksyscalltbl file of LoongArch is
almost same with arm64.

Reviewed-by: Huacai Chen <chenhuacai@loongson.cn>
Reviewed-by: Leo Yan <leo.yan@linaro.org>
Signed-off-by: Tiezhu Yang <yangtiezhu@loongson.cn>
Acked-by: Ian Rogers <irogers@google.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: loongarch@lists.linux.dev
Link: https://lore.kernel.org/r/1685441401-8709-6-git-send-email-yangtiezhu@loongson.cn


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