cmd/go: pass -funwind-tables when compiling C code

Using -funwind-tables is necessary to permit Go code to correctly
throw a panic through C code.  This hasn't been necessary in the past
as -funwind-tables is the default on x86.  However, it is not the
default for PPC AIX.

Change-Id: I4fb1a2d3ab0858ea4e51d3fba1897deb37b5567b
Reviewed-on: https://go-review.googlesource.com/56650
Reviewed-by: Than McIntosh <thanm@google.com>
1 file changed