compiler: Change alias handling, change rune alias to int32.

gcc/go/gofrontend/export.cc

gcc/go/gofrontend/export.h

gcc/go/gofrontend/expressions.cc

gcc/go/gofrontend/expressions.h

gcc/go/gofrontend/gogo.cc

gcc/go/gofrontend/import.cc

gcc/go/gofrontend/lex.cc

gcc/go/gofrontend/lex.h

gcc/go/gofrontend/parse.cc

gcc/go/gofrontend/runtime.cc

gcc/go/gofrontend/runtime.def

gcc/go/gofrontend/statements.cc

gcc/go/gofrontend/types.cc

gcc/go/gofrontend/types.h

gcc/testsuite/go.test/test/fixedbugs/bug204.go

gcc/testsuite/go.test/test/ken/string.go

gcc/testsuite/go.test/test/range.go

gcc/testsuite/go.test/test/solitaire.go

gcc/testsuite/go.test/test/string_lit.go