move BitstreamRemarkParser constructor out of header

Author: Kyle Krueger

llvm/lib/Remarks/BitstreamRemarkParser.cpp

@@ -600,3 +600,5 @@ BitstreamRemarkParser::processRemark(BitstreamRemarkParserHelper &Helper) {
 
   return std::move(Result);
 }
+llvm::remarks::BitstreamRemarkParser::BitstreamRemarkParser(StringRef Buf)
+    : RemarkParser(Format::Bitstream), ParserHelper(Buf) {}

llvm/lib/Remarks/BitstreamRemarkParser.h

@@ -45,8 +45,7 @@ struct BitstreamRemarkParser : public RemarkParser {
 
   /// Create a parser that expects to find a string table embedded in the
   /// stream.
-  explicit BitstreamRemarkParser(StringRef Buf)
-      : RemarkParser(Format::Bitstream), ParserHelper(Buf) {}
+  explicit BitstreamRemarkParser(StringRef Buf);
 
   Expected<std::unique_ptr<Remark>> next() override;