Merge pull request #1687 from swiftlang/hyp/fix-android-sysroot

[android] fix the sysroot linker flag dashes

Author: hyp

Sources/SwiftDriver/Jobs/GenericUnixToolchain+LinkerSupport.swift

@@ -219,10 +219,10 @@ extension GenericUnixToolchain {
 
       if targetTriple.environment == .android {
         if let sysroot = parsedOptions.getLastArgument(.sysroot)?.asSingle {
-          commandLine.appendFlag("-sysroot")
+          commandLine.appendFlag("--sysroot")
           try commandLine.appendPath(VirtualPath(path: sysroot))
         } else if let sysroot = AndroidNDK.getDefaultSysrootPath(in: self.env) {
-          commandLine.appendFlag("-sysroot")
+          commandLine.appendFlag("--sysroot")
           try commandLine.appendPath(VirtualPath(path: sysroot.pathString))
         }
       } else if let path = targetInfo.sdkPath?.path {