libgo: fix improperly mangled linker symbol directive
libgo: fix improperly mangled linker symbol directive

Fix asm name directive for the C version of log/syslog.syslog_c,
which didn't get included in the recent name mangling change.

Change-Id: Ibcee32b955a1ec26cb4a9c9e6aaf10f8bd4b4fb4
Reviewed-on: https://go-review.googlesource.com/c/145017
Reviewed-by: Ian Lance Taylor <87e9c6d529889242b7e184afb632328636553ab4@golang.org>

golang/gofrontend,golang/gofrontend,golang/gofrontend,golang/gofrontend