runtime, runtime/debug: Fix func signature, add missing stubs.

The signature for setGCPercent(int) int has changed between 1.3 and 1.4
to become setGCPercent(int32) int32.
Add missing Entry, FileLine method stubs to runtime.Func struct. This
allows valid Go code to compile.
Merge pull request #140 from shurcooL/master

runtime, runtime/debug: Fix func signature, add missing stubs.