Revert "Rename F_no_mmap to F_mmap" (#134924)

Reverts #134787

Causes the LIT test `lld\test\ELF\link-open-file.test` to fail on the
`llvm-clang-x86_64-sie-win` Build Bot. First instance of the failure
observed in: https://lab.llvm.org/buildbot/#/builders/46/builds/14847

Author: dgg5503

lld/ELF/Arch/ARM.cpp

@@ -1489,7 +1489,7 @@ template <typename ELFT> void elf::writeARMCmseImportLib(Ctx &ctx) {
   const uint64_t fileSize =
       sectionHeaderOff + shnum * sizeof(typename ELFT::Shdr);
   const unsigned flags =
-      ctx.arg.mmapOutputFile ? (unsigned)FileOutputBuffer::F_mmap : 0;
+      ctx.arg.mmapOutputFile ? 0 : (unsigned)FileOutputBuffer::F_no_mmap;
   unlinkAsync(ctx.arg.cmseOutputLib);
   Expected<std::unique_ptr<FileOutputBuffer>> bufferOrErr =
       FileOutputBuffer::create(ctx.arg.cmseOutputLib, fileSize, flags);

lld/ELF/Writer.cpp

@@ -2908,8 +2908,8 @@ template <class ELFT> void Writer<ELFT>::openFile() {
   unsigned flags = 0;
   if (!ctx.arg.relocatable)
     flags |= FileOutputBuffer::F_executable;
-  if (ctx.arg.mmapOutputFile)
-    flags |= FileOutputBuffer::F_mmap;
+  if (!ctx.arg.mmapOutputFile)
+    flags |= FileOutputBuffer::F_no_mmap;
   Expected<std::unique_ptr<FileOutputBuffer>> bufferOrErr =
       FileOutputBuffer::create(ctx.arg.outputFile, fileSize, flags);
 

llvm/include/llvm/Support/FileOutputBuffer.h

@@ -31,8 +31,9 @@ class FileOutputBuffer {
     /// Set the 'x' bit on the resulting file.
     F_executable = 1,
 
-    /// Use mmap for in-memory file buffer.
-    F_mmap = 2,
+    /// Don't use mmap and instead write an in-memory buffer to a file when this
+    /// buffer is closed.
+    F_no_mmap = 2,
   };
 
   /// Factory method to create an OutputBuffer object which manages a read/write

llvm/lib/Support/FileOutputBuffer.cpp

@@ -186,7 +186,7 @@ FileOutputBuffer::create(StringRef Path, size_t Size, unsigned Flags) {
   case fs::file_type::regular_file:
   case fs::file_type::file_not_found:
   case fs::file_type::status_error:
-    if (Flags & F_mmap)
+    if (Flags & F_no_mmap)
       return createInMemoryBuffer(Path, Size, Mode);
     else
       return createOnDiskBuffer(Path, Size, Mode);

llvm/unittests/Support/FileOutputBufferTest.cpp

@@ -123,7 +123,7 @@ TEST(FileOutputBuffer, Test) {
   File5.append("/file5");
   {
     Expected<std::unique_ptr<FileOutputBuffer>> BufferOrErr =
-        FileOutputBuffer::create(File5, 8000, FileOutputBuffer::F_mmap);
+        FileOutputBuffer::create(File5, 8000, FileOutputBuffer::F_no_mmap);
     ASSERT_NO_ERROR(errorToErrorCode(BufferOrErr.takeError()));
     std::unique_ptr<FileOutputBuffer> &Buffer = *BufferOrErr;
     // Start buffer with special header.