cmd/compile: avoid pointers in go.string.* symbols

When creating binaries for dynamic linking, the linker moves
read-only data symbols that contain pointers into relro sections.
It is not setup for handling a go.string symbol moving to relro.

Instead of teaching it how (because go.string symbols with pointers
are unusual anyhow), put the data in a type.. section.

Fixes the android builder.

Change-Id: Ica4722d32241643c060923517b90276ff8ac6b07
Reviewed-on: https://go-review.googlesource.com/21110
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

src/cmd/compile/internal/gc/reflect.go

@@ -533,7 +533,11 @@ func dname(s *Sym, ot int, name, tag string, pkg *Pkg, exported bool) int {
 	if pkg == nil {
 		_, bsym = stringsym(string(b))
 	} else {
-		bsymname := fmt.Sprintf(`go.string."".methodname.%d`, dnameCount)
+		// Write out data as "type.." to signal two things to the
+		// linker, first that when dynamically linking, the symbol
+		// should be moved to a relro section, and second that the
+		// contents should not be decoded as a type.
+		bsymname := fmt.Sprintf(`type..methodname."".%d`, dnameCount)
 		dnameCount++
 		bsym = obj.Linklookup(Ctxt, bsymname, 0)
 		bsym.P = b