Switch gofrontend to using go.googlesource.com, and
update to 81eb6a3f425b2158c67ee32c0cc973a72ce9d6be.
There are various changes required to update to the
go 1.5 runtime:
- typemap.go is changed to accommodate the change in representation for equal/hash algorithms, and the removal of the zero value/type.
- CMakeLists.txt is updated to add the build tree to the package search path, so internal packages, which are not installed, are found.
- various files changes due to removal of __go_new_nopointers; the same change as in D11863, but with NoUnwindAttribute added to the added runtime functions which are called with "callOnly".
- minor cleanups in ssa.go while investigating issues with unwinding/panic handling.