[ABIChecking] Use -Isystem and -Fsystem for swift-api-digester

swift-api-digester is changing to use the Swift -Fsystem flag instead of the clang -iframework flag. It never supported the clang -isystem flag, but it now supports the Swift -Isystem flag.

rdar://152747553

Author: ian-twilightcoder

Sources/SwiftDriver/Jobs/APIDigesterJobs.swift

@@ -193,16 +193,8 @@ extension Driver {
     commandLine.appendFlag(.resourceDir)
     commandLine.appendPath(VirtualPath.lookup(frontendTargetInfo.runtimeResourcePath.path))
 
-    try commandLine.appendAll(.I, from: &parsedOptions)
-    for systemImport in parsedOptions.arguments(for: .Isystem) {
-      commandLine.appendFlag("-isystem")
-      commandLine.appendFlag(systemImport.argument.asSingle)
-    }
-    try commandLine.appendAll(.F, from: &parsedOptions)
-    for systemFramework in parsedOptions.arguments(for: .Fsystem) {
-      commandLine.appendFlag(.iframework)
-      commandLine.appendFlag(systemFramework.argument.asSingle)
-    }
+    try commandLine.appendAll(.I, .Isystem, from: &parsedOptions)
+    try commandLine.appendAll(.F, .Fsystem, from: &parsedOptions)
 
     try commandLine.appendLast(.swiftVersion, from: &parsedOptions)
   }

Sources/SwiftOptions/Options.swift

@@ -600,7 +600,6 @@ extension Option {
   public static let help_: Option = Option("--help", .flag, alias: Option.help, attributes: [.frontend, .autolinkExtract, .moduleWrap, .synthesizeInterface], helpText: "Display available options")
   public static let h: Option = Option("-h", .flag, alias: Option.help)
   public static let IEQ: Option = Option("-I=", .joined, alias: Option.I, attributes: [.frontend, .argumentIsPath])
-  public static let iframework: Option = Option("-iframework", .joinedOrSeparate, attributes: [.noDriver, .argumentIsPath], helpText: "add a directory to the clang importer system framework search path")
   public static let ignoreAlwaysInline: Option = Option("-ignore-always-inline", .flag, attributes: [.helpHidden, .frontend, .noDriver], helpText: "Ignore @inline(__always) attributes.")
   public static let ignoreModuleSourceInfo: Option = Option("-ignore-module-source-info", .flag, attributes: [.frontend, .noDriver], helpText: "Avoid getting source location from .swiftsourceinfo files")
   public static let ignoreSpiGroups: Option = Option("-ignore-spi-group", .separate, attributes: [.noDriver], helpText: "SPI group name to not diagnose about")
@@ -1564,7 +1563,6 @@ extension Option {
       Option.help_,
       Option.h,
       Option.IEQ,
-      Option.iframework,
       Option.ignoreAlwaysInline,
       Option.ignoreModuleSourceInfo,
       Option.ignoreSpiGroups,