[COFF] Refactor section alignment calculation

Section alignment isn't completely trivial, let it live in one place so
that we may reuse it in LLVM.

llvm-svn: 263722

llvm/lib/Object/COFFObjectFile.cpp

@@ -290,7 +290,7 @@ std::error_code COFFObjectFile::getSectionContents(DataRefImpl Ref,
 
 uint64_t COFFObjectFile::getSectionAlignment(DataRefImpl Ref) const {
   const coff_section *Sec = toSec(Ref);
-  return uint64_t(1) << (((Sec->Characteristics & 0x00F00000) >> 20) - 1);
+  return Sec->getAlignment();
 }
 
 bool COFFObjectFile::isSectionText(DataRefImpl Ref) const {