runtime, syscall: use full prototypes in C code

Based on patch by Martin Sebor.

For GCC PR 82922.

Change-Id: I66feffa1a9266e83c56183868de5d726cff33fd0
Reviewed-on: https://go-review.googlesource.com/86815
Reviewed-by: Than McIntosh <thanm@google.com>
Reviewed-by: Ian Lance Taylor <iant@golang.org>
5 files changed