[Lex] Use llvm::byteswap instead of sys::getSwappedBytes (NFC)

Author: kazutakahirata

clang/lib/Lex/HeaderMap.cpp

@@ -87,9 +87,8 @@ bool HeaderMapImpl::checkHeader(const llvm::MemoryBuffer &File,
 
   // Check the number of buckets.  It should be a power of two, and there
   // should be enough space in the file for all of them.
-  uint32_t NumBuckets = NeedsByteSwap
-                            ? llvm::sys::getSwappedBytes(Header->NumBuckets)
-                            : Header->NumBuckets;
+  uint32_t NumBuckets =
+      NeedsByteSwap ? llvm::byteswap(Header->NumBuckets) : Header->NumBuckets;
   if (!llvm::isPowerOf2_32(NumBuckets))
     return false;
   if (File.getBufferSize() <

clang/unittests/Lex/HeaderMapTestUtils.h

@@ -33,11 +33,10 @@ template <unsigned NumBuckets, unsigned NumBytes> struct HMapFileMock {
   }
 
   void swapBytes() {
-    using llvm::sys::getSwappedBytes;
-    Header.Magic = getSwappedBytes(Header.Magic);
-    Header.Version = getSwappedBytes(Header.Version);
-    Header.NumBuckets = getSwappedBytes(Header.NumBuckets);
-    Header.StringsOffset = getSwappedBytes(Header.StringsOffset);
+    Header.Magic = llvm::byteswap(Header.Magic);
+    Header.Version = llvm::byteswap(Header.Version);
+    Header.NumBuckets = llvm::byteswap(Header.NumBuckets);
+    Header.StringsOffset = llvm::byteswap(Header.StringsOffset);
   }
 
   std::unique_ptr<llvm::MemoryBuffer> getBuffer() {