DTLTO Cache optimization

Currently, DTLTO cache works this way: when native object file is
generated and sent back by the remote compilation, it's being saved on
the disk, then the content of this file is read and written into a
buffer and subsequently it's read from the buffer and written into the
cache file. This is obviously non-efficient.

With this optimization, after the native object file is saved on the
disk, it's being renamed into a cache file.

GitOrigin-RevId: c562f17fe5607e94f85a996fd631803f3ba71122

COFF/LTO.cpp

diff --git a/COFF/LTO.cpp b/COFF/LTO.cpp
index f85a260..0e335d6 100644
--- a/COFF/LTO.cpp
+++ b/COFF/LTO.cpp
@@ -216,7 +216,8 @@
   FileCache cache;
   if (!ctx.config.ltoCache.empty())
     cache = check(localCache("ThinLTO", "Thin", ctx.config.ltoCache,
-                             createAddBufferFn(files, file_names)));
+                             createAddBufferFn(files, file_names),
+                             !ctx.config.dtltoDistributor.empty()));
 
   checkError(ltoObj->run(
       [&](size_t task, const Twine &moduleName) {

ELF/LTO.cpp

diff --git a/ELF/LTO.cpp b/ELF/LTO.cpp
index a116811..f76d605 100644
--- a/ELF/LTO.cpp
+++ b/ELF/LTO.cpp
@@ -341,7 +341,8 @@
   FileCache cache;
   if (!ctx.arg.thinLTOCacheDir.empty())
     cache = check(localCache("ThinLTO", "Thin", ctx.arg.thinLTOCacheDir,
-                             createAddBufferFn(files, filenames)));
+                             createAddBufferFn(files, filenames),
+                             !ctx.arg.dtltoDistributor.empty()));
 
   if (!ctx.bitcodeFiles.empty())
     checkError(ctx.e, ltoObj->run(