A couple of readASTFileSignature improvements (NFC)

* Strength reduce a std::function to a function pointer,
* Factor out checking the AST file magic number,
* Add a brief doc comment to readAStFileSignature

Thanks to Chandler for spotting these oddities.

llvm-svn: 233050

1 files changed, 1 insertions, 2 deletions

diff --git a/clang/lib/Serialization/ModuleManager.cpp b/clang/lib/Serialization/ModuleManager.cpp
index b073984..a50c2b1 100644
--- a/clang/lib/Serialization/ModuleManager.cpp
+++ b/clang/lib/Serialization/ModuleManager.cpp
@@ -58,8 +58,7 @@ ModuleManager::addModule(StringRef FileName, ModuleKind Type,
                          unsigned Generation,
                          off_t ExpectedSize, time_t ExpectedModTime,
                          ASTFileSignature ExpectedSignature,
-                         std::function<ASTFileSignature(llvm::BitstreamReader &)>
-                             ReadSignature,
+                         ASTFileSignatureReader ReadSignature,
                          ModuleFile *&Module,
                          std::string &ErrorStr) {
   Module = nullptr;