Don't normalize *-unknown-windows-coff as *-unknown-windows-msvc (#1558)

Author: MaxDesiatov

Sources/SwiftDriver/Utilities/Triple.swift

@@ -126,7 +126,7 @@ public struct Triple {
         parser.components.resize(toCount: 4, paddingWith: "")
         parser.components[2] = "windows"
         if parsedEnv?.value.environment == nil {
-          if let objectFormat = parsedEnv?.value.objectFormat, objectFormat != .coff {
+          if let objectFormat = parsedEnv?.value.objectFormat {
             parser.components[3] = Substring(objectFormat.name)
           } else {
             parser.components[3] = "msvc"

Tests/SwiftDriverTests/TripleTests.swift

@@ -816,6 +816,9 @@ final class TripleTests: XCTestCase {
 
     assertNormalizesEqual("i686-pc-windows-elf-elf",
               "i686-pc-windows-elf")
+
+    assertNormalizesEqual("i686-unknown-windows-coff", "i686-unknown-windows-coff")
+    assertNormalizesEqual("x86_64-unknown-windows-coff", "x86_64-unknown-windows-coff")
   }
 
   func testNormalizeARM() {
@@ -1065,6 +1068,7 @@ final class TripleTests: XCTestCase {
     XCTAssertEqual(.macho, Triple("i686---macho").objectFormat)
 
     XCTAssertEqual(.coff, Triple("i686--win32").objectFormat)
+    XCTAssertEqual(.coff, Triple("i686-unknown-windows-coff").objectFormat)
 
     XCTAssertEqual(.elf, Triple("i686-pc-windows-msvc-elf").objectFormat)
     XCTAssertEqual(.elf, Triple("i686-pc-cygwin-elf").objectFormat)