Fix a gsym warning on Windows

[aganea]

Summary

Use a 64-bit integer for Length instead of off_t which is defined as a long on Windows.

(from C:\Program Files (x86)\Windows Kits\10\Include\10.0.18362.0\ucrt\sys\types.h)

#ifndef _OFF_T_DEFINED
    #define _OFF_T_DEFINED

    typedef long _off_t; // file offset value

    #if (defined _CRT_DECLARE_NONSTDC_NAMES && _CRT_DECLARE_NONSTDC_NAMES) || (!defined _CRT_DECLARE_NONSTDC_NAMES && !__STDC__)
        typedef _off_t off_t;
    #endif
#endif

This fixes:

F:\llvm-project\llvm\lib\DebugInfo\GSYM\FunctionInfo.cpp(118,16): warning: comparison of integers of different signs: 'const off_t' (aka 'const long') and 'unsigned int' [-Wsign-compare]
    if (Length > UINT32_MAX)
        ~~~~~~ ^ ~~~~~~~~~~
F:\llvm-project\llvm\lib\DebugInfo\GSYM\FunctionInfo.cpp(136,16): warning: comparison of integers of different signs: 'const off_t' (aka 'const long') and 'unsigned int' [-Wsign-compare]
    if (Length > UINT32_MAX)
        ~~~~~~ ^ ~~~~~~~~~~

[aganea]

Fixed by rG22d41ba024fa08026ebd85ec842712fcf780ca2a

llvm/lib/DebugInfo/GSYM/FunctionInfo.cpp

if (OptLineTable.hasValue()) {
     O.writeU32(InfoType::LineTableInfo);
     // Write a uint32_t length as zero for now, we will fix this up after
     // writing the LineTable out with the number of bytes that were written.
     O.writeU32(0);
     const auto StartOffset = O.tell();
     llvm::Error err = OptLineTable->encode(O, Range.Start);
     if (err)
       return std::move(err);
-    const off_t Length = O.tell() - StartOffset;
+    const uint64_t Length = O.tell() - StartOffset;
     if (Length > UINT32_MAX)
         return createStringError(std::errc::invalid_argument,
             "LineTable length is greater than UINT32_MAX");
     // Fixup the size of the LineTable data with the correct size.
     O.fixup32(static_cast<uint32_t>(Length), StartOffset - 4);
   }
 
   // Write out the inline function info if we have any and if it is valid.
   if (Inline.hasValue()) {
     O.writeU32(InfoType::InlineInfo);
     // Write a uint32_t length as zero for now, we will fix this up after
     // writing the LineTable out with the number of bytes that were written.
     O.writeU32(0);
     const auto StartOffset = O.tell();
     llvm::Error err = Inline->encode(O, Range.Start);
     if (err)
       return std::move(err);
-    const off_t Length = O.tell() - StartOffset;
+    const uint64_t Length = O.tell() - StartOffset;
     if (Length > UINT32_MAX)
         return createStringError(std::errc::invalid_argument,
             "InlineInfo length is greater than UINT32_MAX");
     // Fixup the size of the InlineInfo data with the correct size.
     O.fixup32(static_cast<uint32_t>(Length), StartOffset - 4);
   }
 
   // Terminate the data chunks with and end of list with zero size
   O.writeU32(InfoType::EndOfList);
   O.writeU32(0);
   return FuncInfoOffset;
 }