Fix test/Misc/target-cpu.swift (#81137)

It expected `apple-a7`, while the new value is `apple-a4` for `WATCHTARGETCPU2`.

rdar://150074485

Author: MaxDesiatov

test/Misc/target-cpu.swift

@@ -13,8 +13,8 @@
 // RUN: not %swift -typecheck -target armv7k-apple-watchos2 -Xcc -### %s 2>&1 | %FileCheck -check-prefix=WATCHTARGETCPU1 %s
 // WATCHTARGETCPU1: "-target-cpu" "cortex-a7"
 
-// RUN: not %swift -typecheck -target arm64-apple-watchos2 -Xcc -### %s 2>&1 | %FileCheck -check-prefix=WATCHTARGETCPU2 %s
-// WATCHTARGETCPU2: "-target-cpu" "apple-a7"
+// RUN: not %swift -typecheck -target arm64_32-apple-watchos2 -Xcc -### %s 2>&1 | %FileCheck -check-prefix=WATCHTARGETCPU2 %s
+// WATCHTARGETCPU2: "-target-cpu" "apple-s4"
 
 // RUN: not %swift -typecheck -target armv7s-apple-ios7 -Xcc -### %s 2>&1 | %FileCheck -check-prefix=TARGETCPU2 %s
 // TARGETCPU2: "-target-cpu" "swift"