Address reviewer feedback.

 - Do .str() around the full string concatenation
 - Reorganize test

Author: rjmansfield

llvm/lib/ObjectYAML/MachOEmitter.cpp

@@ -305,8 +305,8 @@ void MachOWriter::writeLoadCommands(raw_ostream &OS) {
       if (NameCStr)
         Name = NameCStr;
       else
-        Name =
-            "(0x" + Twine::utohexstr(LC.Data.load_command_data.cmd).str() + ")";
+        Name = ("(0x" + Twine::utohexstr(LC.Data.load_command_data.cmd) + ")")
+                   .str();
 
       WithColor::warning() << "load command " << i << " " << Name
                            << " cmdsize too small ("

llvm/test/ObjectYAML/MachO/load-cmdsize-too-small.yaml

@@ -1,18 +1,13 @@
 ## Test that yaml2obj handles load commands with cmdsize smaller than the
 ## actual structure size without crashing (due to integer underflow).
 
+## Test with a known load command (LC_SEGMENT_64).
 # RUN: yaml2obj %s --docnum=1 -o %t1 2>&1 | FileCheck %s --check-prefix=WARNING-KNOWN
 # RUN: not llvm-readobj --file-headers %t1 2>&1 | FileCheck %s --check-prefix=MALFORMED
 
-# RUN: yaml2obj %s --docnum=2 -o %t2 2>&1 | FileCheck %s --check-prefix=WARNING-UNKNOWN
-
 # WARNING-KNOWN: warning: load command 0 LC_SEGMENT_64 cmdsize too small (56 bytes) for actual size (72 bytes)
 
 # MALFORMED: error: {{.*}}: truncated or malformed object (load command 0 LC_SEGMENT_64 cmdsize too small)
-
-# WARNING-UNKNOWN: warning: load command 0 (0xdeadbeef) cmdsize too small (8 bytes) for actual size (20 bytes)
-
-## Test with a known load command (LC_SEGMENT_64)
 --- !mach-o
 FileHeader:
   magic:           0xFEEDFACF
@@ -37,7 +32,10 @@ LoadCommands:
     flags:           0
 ...
 
-## Test with an unknown load command value
+## Test with an unknown load command value.
+# RUN: yaml2obj %s --docnum=2 -o %t2 2>&1 | FileCheck %s --check-prefix=WARNING-UNKNOWN
+
+# WARNING-UNKNOWN: warning: load command 0 (0xdeadbeef) cmdsize too small (8 bytes) for actual size (20 bytes)
 --- !mach-o
 FileHeader:
   magic:           0xFEEDFACF