misc/ios: don't refer to iostest.bash

iostest.bash might not live much longer, and all.bash is much
less confusing and more explicit.

Change-Id: If42e8716bbbb02aa3f817dceaabb1aa8076aae1a
Reviewed-on: https://go-review.googlesource.com/c/go/+/175178Reviewed-by: Tobias Klauser <tobias.klauser@gmail.com>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

misc/ios/README

@@ -31,9 +31,10 @@ which will output something similar to
 If you have multiple devices connected, specify the device UDID with the GOIOS_DEVICE_ID
 variable. Use `idevice_id -l` to list all available UDIDs.
 
-Finally, to run the standard library tests, run iostest.bash with GOARCH set. For example,
+Finally, to run the standard library tests, run all.bash as usual, but with the compiler
+set to the clang wrapper that invokes clang for iOS. For example,
 
-	GOARCH=arm64 ./iostest.bash
+	GOARCH=arm64 CGO_ENABLED=1 CC_FOR_TARGET=$(pwd)/../misc/ios/clangwrap.sh ./all.bash
 
 To use the go tool directly to run programs and tests, put $GOROOT/bin into PATH to ensure
 the go_darwin_$GOARCH_exec wrapper is found. For example, to run the archive/tar tests