[llvm] Introduce LDBG_OS() macro as a variant of LDBG() (PR #157194)

[Mehdi Amini via llvm-commits]

================
@@ -128,6 +128,131 @@ TEST(DebugLogTest, DestructorPrefix) {
   // After destructors, nothing should have been printed.
   EXPECT_EQ(os.str(), "");
 }
+
+TEST(DebugLogTest, LDBG_MACROS) {
----------------
joker-eph wrote:

gtest prints the line number and the detail of a failing comparison. 
e.g. if I intentionally break one of the reference output:

```
[ RUN      ] DebugLogTest.LDBG_MACROS
llvm/unittests/Support/DebugLogTest.cpp:146: Failure
Expected equality of these values:
  DebugOs.str()
    Which is: "[A:1] DebugLogTest.cpp:143 Hello, world!\n"
  RefOs.str()
    Which is: "[A:2] DebugLogTest.cpp:143 Hello, world!\n"
```

Clicking on the file/line leads directly to the offending EXPECT_EQ.

https://github.com/llvm/llvm-project/pull/157194