_SwiftSyntaxCShims: rename Swift getter

`_errno` is a C reserved identifier. Windows uses this reserved
namespace and results in a collision. Rename the getter to namespace it
and avoid the collision.

Author: compnerd

Sources/SwiftCompilerPluginMessageHandling/StandardIOMessageConnection.swift

@@ -62,27 +62,27 @@ public struct StandardIOMessageConnection: MessageConnection {
     // receiving messages from the plugin host.
     let inputFD = dup(fileno(_stdin))
     guard inputFD >= 0 else {
-      throw IOError.systemError(function: "dup(fileno(stdin))", errno: _errno)
+      throw IOError.systemError(function: "dup(fileno(stdin))", errno: _swift_syntax_errno)
     }
 
     // Having duplicated the original standard-input descriptor, we close
     // `stdin` so that attempts by the plugin to read console input (which
     // are usually a mistake) return errors instead of blocking.
     guard close(fileno(_stdin)) >= 0 else {
-      throw IOError.systemError(function: "close(fileno(stdin))", errno: _errno)
+      throw IOError.systemError(function: "close(fileno(stdin))", errno: _swift_syntax_errno)
     }
 
     // Duplicate the `stdout` file descriptor, which we will then use for
     // sending messages to the plugin host.
     let outputFD = dup(fileno(_stdout))
     guard outputFD >= 0 else {
-      throw IOError.systemError(function: "dup(fileno(stdout))", errno: _errno)
+      throw IOError.systemError(function: "dup(fileno(stdout))", errno: _swift_syntax_errno)
     }
 
     // Having duplicated the original standard-output descriptor, redirect
     // `stdout` to `stderr` so that all free-form text output goes there.
     guard dup2(fileno(_stderr), fileno(_stdout)) >= 0 else {
-      throw IOError.systemError(function: "dup2(fileno(stderr), fileno(stdout))", errno: _errno)
+      throw IOError.systemError(function: "dup2(fileno(stderr), fileno(stdout))", errno: _swift_syntax_errno)
     }
 
     #if canImport(ucrt)
@@ -101,7 +101,7 @@ public struct StandardIOMessageConnection: MessageConnection {
     let endPtr = ptr.advanced(by: buffer.count)
     while ptr != endPtr {
       switch write(outputFileDescriptor, ptr, numericCast(endPtr - ptr)) {
-      case -1: throw IOError.systemError(function: "write(_:_:_:)", errno: _errno)
+      case -1: throw IOError.systemError(function: "write(_:_:_:)", errno: _swift_syntax_errno)
       case 0: throw IOError.systemError(function: "write", errno: 0) /* unreachable */
       case let n: ptr += Int(n)
       }
@@ -116,7 +116,7 @@ public struct StandardIOMessageConnection: MessageConnection {
     let endPtr = ptr.advanced(by: buffer.count)
     while ptr != endPtr {
       switch read(inputFileDescriptor, ptr, numericCast(endPtr - ptr)) {
-      case -1: throw IOError.systemError(function: "read(_:_:_:)", errno: _errno)
+      case -1: throw IOError.systemError(function: "read(_:_:_:)", errno: _swift_syntax_errno)
       case 0: throw IOError.readReachedEndOfInput
       case let n: ptr += Int(n)
       }

Sources/_SwiftSyntaxCShims/include/swiftsyntax_errno.h

@@ -17,7 +17,7 @@
 
 #include <errno.h>
 
-SWIFT_NAME_S("getter:_errno()")
+SWIFT_NAME_S("getter:_swift_syntax_errno()")
 static inline int swiftsyntax_errno(void) {
   return errno;
 }