runtime: flag static variables as no-pointers

runtime: flag static variables as no-pointers

Variables in data sections of 32-bit executables interfere with
garbage collector's ability to free objects and/or unnecessarily
slow down the garbage collector.

This changeset moves some static variables to .noptr sections.
'files' in symtab.c is now allocated dynamically.

R=golang-dev, dvyukov, minux.ma
CC=golang-dev
https://golang.org/cl/9786044