runtime: add ppc and s390 to 32 build constraints for gccgo

Theses are not supported by the go compiler but it may helps porting to gccgo.

I have no idea if this change is correct, but it is weird that
os_linux32.go and os_linux64.go should have ppc & s390 but not all other
files gated to 32bits in the same package.

Change-Id: I0bb70cdb88c19096386320d02d546942263e009d
Reviewed-on: https://go-review.googlesource.com/c/go/+/714082
Reviewed-by: Ian Lance Taylor <iant@golang.org>
Reviewed-by: David Chase <drchase@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Auto-Submit: Jorropo <jorropo.pgm@gmail.com>
Reviewed-by: Dmitri Shuralyov <dmitshur@google.com>

Author: Jorropo

src/runtime/hash32.go

@@ -5,7 +5,7 @@
 // Hashing algorithm inspired by
 // wyhash: https://github.com/wangyi-fudan/wyhash/blob/ceb019b530e2c1c14d70b79bfa2bc49de7d95bc1/Modern%20Non-Cryptographic%20Hash%20Function%20and%20Pseudorandom%20Number%20Generator.pdf
 
-//go:build 386 || arm || mips || mipsle || wasm
+//go:build 386 || arm || mips || mipsle || wasm || (gccgo && (ppc || s390))
 
 package runtime
 

src/runtime/mpagealloc_32bit.go

@@ -2,7 +2,7 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
-//go:build 386 || arm || mips || mipsle || wasm
+//go:build 386 || arm || mips || mipsle || wasm || (gccgo && (ppc || s390))
 
 // wasm is a treated as a 32-bit architecture for the purposes of the page
 // allocator, even though it has 64-bit pointers. This is because any wasm

src/runtime/panic32.go

@@ -2,7 +2,7 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
-//go:build 386 || arm || mips || mipsle
+//go:build 386 || arm || mips || mipsle || (gccgo && (ppc || s390))
 
 package runtime
 

src/runtime/tagptr_32bit.go

@@ -2,7 +2,7 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
-//go:build 386 || arm || mips || mipsle
+//go:build 386 || arm || mips || mipsle || (gccgo && (ppc || s390))
 
 package runtime