Windows: migrate to CRT from MSVCRT (#249)

The Windows environment calls the library `CRT`.  This also enables the
removal of the `visualc` module from the Swift SDK overlay.

Author: compnerd

Sources/ArgumentParser/Completions/CompletionsGenerator.swift

@@ -13,8 +13,8 @@
 import Glibc
 #elseif canImport(Darwin)
 import Darwin
-#elseif canImport(MSVCRT)
-import MSVCRT
+#elseif canImport(CRT)
+import CRT
 #endif
 
 /// A shell for which the parser can generate a completion script.

Sources/ArgumentParser/Parsable Properties/Errors.swift

@@ -13,8 +13,8 @@
 import Glibc
 #elseif canImport(Darwin)
 import Darwin
-#elseif canImport(MSVCRT)
-import MSVCRT
+#elseif canImport(CRT)
+import CRT
 #endif
 
 #if os(Windows)

Sources/ArgumentParser/Parsable Types/ParsableArguments.swift

@@ -15,8 +15,8 @@ let _exit: (Int32) -> Never = Glibc.exit
 #elseif canImport(Darwin)
 import Darwin
 let _exit: (Int32) -> Never = Darwin.exit
-#elseif canImport(MSVCRT)
-import MSVCRT
+#elseif canImport(CRT)
+import CRT
 let _exit: (Int32) -> Never = ucrt._exit
 #endif
 

Sources/ArgumentParser/Usage/HelpGenerator.swift

@@ -298,8 +298,8 @@ func ioctl(_ a: Int32, _ b: Int32, _ p: UnsafeMutableRawPointer) -> Int32 {
 }
 #elseif canImport(Darwin)
 import Darwin
-#elseif canImport(MSVCRT)
-import MSVCRT
+#elseif canImport(CRT)
+import CRT
 import WinSDK
 #endif