Emit debug info for global variables first.

This works around a limitation in gdb which is reported by following inherit.exp test failures from gdb testsuite.

gdb.cp/inherit.exp: print g_vB.vB::vb
gdb.cp/inherit.exp: print g_vB.vB::vx
gdb.cp/inherit.exp: print g_vC.vC::vc
gdb.cp/inherit.exp: print g_vC.vC::vx
gdb.cp/inherit.exp: print g_vD.vB::vb
...

llvm-svn: 130702