[ASTGen] Fix a couple of @_cdecl param types

These are `void *` on the C side.

Author: hamishknight

lib/ASTGen/Sources/ASTGen/ASTGen.swift

@@ -476,7 +476,7 @@ extension Optional where Wrapped: LazyCollectionProtocol {
 /// Generate AST nodes for all top-level entities in the given source file.
 @_cdecl("swift_ASTGen_buildTopLevelASTNodes")
 public func buildTopLevelASTNodes(
-  diagEnginePtr: UnsafeMutablePointer<UInt8>,
+  diagEnginePtr: UnsafeMutableRawPointer,
   sourceFilePtr: UnsafePointer<UInt8>,
   dc: UnsafeMutableRawPointer,
   ctx: UnsafeMutableRawPointer,

lib/ASTGen/Sources/ASTGen/SourceFile.swift

@@ -102,7 +102,7 @@ extension Syntax {
 /// Emit diagnostics within the given source file.
 @_cdecl("swift_ASTGen_emitParserDiagnostics")
 public func emitParserDiagnostics(
-  diagEnginePtr: UnsafeMutablePointer<UInt8>,
+  diagEnginePtr: UnsafeMutableRawPointer,
   sourceFilePtr: UnsafeMutablePointer<UInt8>,
   emitOnlyErrors: CInt,
   downgradePlaceholderErrorsToWarnings: CInt

lib/ASTGen/Sources/ASTGen/Types.swift

@@ -342,7 +342,7 @@ extension ASTGenVisitor {
 @_cdecl("swift_ASTGen_buildTypeRepr")
 @usableFromInline
 func buildTypeRepr(
-  diagEnginePtr: UnsafeMutablePointer<UInt8>,
+  diagEnginePtr: UnsafeMutableRawPointer,
   sourceFilePtr: UnsafeRawPointer,
   typeLocPtr: UnsafePointer<UInt8>,
   dc: UnsafeMutableRawPointer,