[clang] [clang-tools-extra] [Clang] Treat line directives as header names. (PR #211512)

[Aaron Ballman via cfe-commits]

================
@@ -75,9 +75,21 @@ extern int z;
 # 44 "A.c"
 # 49 "A.c"
 
-// CHECK: # 50 "a\n.c"
+// CHECK: # 50 "a\\n.c"
 # 50 "a\n.c"
 
+// CHECK: # 1 "c:\\moo\\zar\\haz.h"
+#line 1 "c:\moo\zar\haz.h"
+
+// CHECK # 1 "original\x12source.c"
+# 1 "original\x12source.c"
+
+// CHECK # 1 "original\u1234"
+# 1 "original\u1234"
+
+// CHECK # 1 "original\u{1234}"
+# 1 "original\u{1234}"
----------------
AaronBallman wrote:

We should also add test coverage for:
```
#line 12 <foo.c>
```
and other angle bracket variants?

https://github.com/llvm/llvm-project/pull/211512