ld: fix alignment of rodata section on Plan 9

This was causing a panic in the reflect package
since type.* pointers with their low bits set are
assumed to have certain flags set that disallow
the use of reflection.

Thanks to Pavel and Taru for help tracking down
this bug.

R=rsc, paulzhol, taruti
CC=golang-dev
https://golang.org/cl/4511041
2 files changed