[Bug go/56431] -lpthread should be added to -lgo

[hjl.tools at gmail dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=56431

--- Comment #2 from H.J. Lu <hjl.tools at gmail dot com> 2013-02-27 16:59:17 UTC ---
The new GNU ld is complaining about an undefined weak reference because
it sees libpthread.so from DT_NEEDED in libgo.so. The old GNU ld just
silently adds libpthread.so from DT_NEEDED in libgo.so.  When creating
executables, GNU ld checks DT_NEEDED in DSOes on command line.  Since
libpthread.so is included from libgo.so for creating executables, it expects
libpthread.so will be used and pthread_sigmask is defined at run-time