[SystemZ][z/OS] Open YAML files for read as text files (#121340)

This patch makes sure YAML files are opened for reading as text file to
trigger auto-conversion from EBCDIC encoding into expected ASCII
encoding on z/OS platform. This is required to fix the following lit
tests:

```
LLVM :: tools/llvm-gsymutil/ARM_AArch64/macho-gsym-callsite-info-exe.yaml
LLVM :: tools/llvm-gsymutil/ARM_AArch64/macho-gsym-callsite-info-obj.test
LLVM :: tools/llvm-gsymutil/ARM_AArch64/macho-gsym-callsite-info-dsym.yaml
LLVM :: Transforms/PGOProfile/memprof_undrift_missing_leaf.ll
```

Author: zibi2

llvm/lib/DebugInfo/GSYM/CallSiteInfo.cpp

@@ -151,7 +151,7 @@ LLVM_YAML_IS_SEQUENCE_VECTOR(FunctionYAML)
 
 Error CallSiteInfoLoader::loadYAML(StringRef YAMLFile) {
   // Step 1: Read YAML file
-  auto BufferOrError = MemoryBuffer::getFile(YAMLFile);
+  auto BufferOrError = MemoryBuffer::getFile(YAMLFile, /*IsText=*/true);
   if (!BufferOrError)
     return errorCodeToError(BufferOrError.getError());
 

llvm/lib/ProfileData/MemProfReader.cpp

@@ -754,7 +754,7 @@ Error RawMemProfReader::readNextRecord(
 
 Expected<std::unique_ptr<YAMLMemProfReader>>
 YAMLMemProfReader::create(const Twine &Path) {
-  auto BufferOr = MemoryBuffer::getFileOrSTDIN(Path);
+  auto BufferOr = MemoryBuffer::getFileOrSTDIN(Path, /*IsText=*/true);
   if (std::error_code EC = BufferOr.getError())
     return report(errorCodeToError(EC), Path.getSingleStringRef());
 
@@ -770,7 +770,7 @@ YAMLMemProfReader::create(std::unique_ptr<MemoryBuffer> Buffer) {
 }
 
 bool YAMLMemProfReader::hasFormat(const StringRef Path) {
-  auto BufferOr = MemoryBuffer::getFileOrSTDIN(Path);
+  auto BufferOr = MemoryBuffer::getFileOrSTDIN(Path, /*IsText=*/true);
   if (!BufferOr)
     return false;