Merge pull request swiftlang#2638 from ahoppen/rename-stdio-errno

Rename `errno.h` and `stdio.h` to `swiftsyntax_errno.h` and `swiftsyntax_stdio.h`

Author: ahoppen

Sources/_SwiftSyntaxCShims/include/swiftsyntax/AtomicBool.h renamed to Sources/_SwiftSyntaxCShims/include/AtomicBool.h

@@ -1,7 +1,7 @@
 module _SwiftSyntaxCShims {
-  header "swiftsyntax/_includes.h"
-  header "swiftsyntax/AtomicBool.h"
-  header "swiftsyntax/errno.h"
-  header "swiftsyntax/stdio.h"
+  header "_includes.h"
+  header "AtomicBool.h"
+  header "swiftsyntax_errno.h"
+  header "swiftsyntax_stdio.h"
   export *
 }