[SE-0458] Drop "unsafe" effect for for..in loop in inlined code in interfaces

Only compilers can't handle it, so drop it for now.

Author: DougGregor

lib/ASTGen/Sources/ASTGen/CompilerBuildConfiguration.swift

@@ -552,6 +552,10 @@ fileprivate class RemoveUnsafeExprSyntaxRewriter: SyntaxRewriter {
   override func visit(_ node: UnsafeExprSyntax) -> ExprSyntax {
     return node.expression.with(\.leadingTrivia, node.leadingTrivia)
   }
+
+  override func visit(_ node: ForStmtSyntax) -> StmtSyntax {
+    return StmtSyntax(node.with(\.unsafeKeyword, nil))
+  }
 }
 
 extension SyntaxProtocol {

test/Unsafe/module-interface.swift

@@ -9,10 +9,21 @@
 // CHECK: #endif
 @unsafe public func getIntUnsafely() -> Int { 0 }
 
+public struct UnsafeIterator: @unsafe IteratorProtocol {
+  @unsafe public mutating func next() -> Int? { nil }
+}
+
+public struct SequenceWithUnsafeIterator: Sequence {
+  public init() { }
+  public func makeIterator() -> UnsafeIterator { UnsafeIterator() }
+}
+
 // CHECK: @inlinable public func useUnsafeCode()
 @inlinable public func useUnsafeCode() {
   // CHECK-NOT: unsafe
   print( unsafe getIntUnsafely())
+
+  for unsafe _ in SequenceWithUnsafeIterator() { }
 }
 
 // CHECK: public protocol P