cmd/dist, internal/platform: remove some target modes that fail

Before CL 463992 there were some cases that cmd/dist did not test
but that platform.BuildModeSupport permitted. In CL 463992 those
conflicts were resolved in favor of platform.BuildModeSupport.
However, further testing has uncovered some cases that do not in
fact work. Adjust those in both cmd/dist and internal/platform.

In particular, mark android-arm and android-arm64 as not supporting
plugin mode.  Sample failure:
    https://build.golang.org/log/ebba858ea9f94f076966d8cfd42348a0e9345095

Mark ios as not supporting c-archive mode.  Sample failure:
    https://build.golang.org/log/e78a58189d94b90dc6d4b2e01a1b4a0b35d63792

Fixes #58170
Fixes #58172

Change-Id: Ic1bd18e36382cac0779aad48cb6e7b1de8eeb10d
Reviewed-on: https://go-review.googlesource.com/c/go/+/464339
Reviewed-by: Bryan Mills <[email protected]>
Run-TryBot: Ian Lance Taylor <[email protected]>
Auto-Submit: Ian Lance Taylor <[email protected]>
Run-TryBot: Ian Lance Taylor <[email protected]>
Reviewed-by: Ian Lance Taylor <[email protected]>
TryBot-Result: Gopher Robot <[email protected]>

Author: ianlancetaylor

src/cmd/dist/test.go

@@ -1143,7 +1143,7 @@ func (t *tester) supportedBuildmode(mode string) bool {
 			return false
 		}
 		switch goos {
-		case "aix", "darwin", "ios", "windows":
+		case "aix", "darwin", "windows":
 			return true
 		case "linux":
 			switch goarch {
@@ -1182,7 +1182,7 @@ func (t *tester) supportedBuildmode(mode string) bool {
 		switch pair {
 		case "linux-386", "linux-amd64", "linux-arm", "linux-arm64", "linux-s390x", "linux-ppc64le":
 			return true
-		case "android-386", "android-amd64", "android-arm", "android-arm64":
+		case "android-386", "android-amd64":
 			return true
 		case "darwin-amd64", "darwin-arm64":
 			return true

src/internal/platform/supported.go

@@ -101,7 +101,7 @@ func BuildModeSupported(compiler, buildmode, goos, goarch string) bool {
 
 	case "c-archive":
 		switch goos {
-		case "aix", "darwin", "ios", "windows":
+		case "aix", "darwin", "windows":
 			return true
 		case "linux":
 			switch goarch {
@@ -163,7 +163,7 @@ func BuildModeSupported(compiler, buildmode, goos, goarch string) bool {
 	case "plugin":
 		switch platform {
 		case "linux/amd64", "linux/arm", "linux/arm64", "linux/386", "linux/s390x", "linux/ppc64le",
-			"android/amd64", "android/arm", "android/arm64", "android/386",
+			"android/amd64", "android/386",
 			"darwin/amd64", "darwin/arm64",
 			"freebsd/amd64":
 			return true