[COFF] Stop lowercasing paths in messages

[smeenai]

Summary

It's pretty annoying to have LLD lowercase paths in error messages when
cross-compiling from a case-sensitive filesystem, since e.g. if I want
to examine the problematic object file, I have to perform some manual
case correction instead of just being able to copy the path from the
error message.

[ruiu]

LGTM

I believe it is me who wrote code to lowercase pathnames, but I don't remember why I decided to do that.

COFF/InputFiles.cpp

static StringRef getBasename(StringRef Path) {
   return Path.substr(Pos + 1);
 }
 
 // Returns a string in the format of "foo.obj" or "foo.obj(bar.lib)".
 std::string lld::toString(const coff::InputFile *File) {
   if (!File)
     return "<internal>";
   if (File->ParentName.empty())
-    return File->getName().lower();
+    return File->getName();
 
-  std::string Res =
-      (getBasename(File->ParentName) + "(" + getBasename(File->getName()) + ")")
-          .str();
-  return StringRef(Res).lower();
+  return (getBasename(File->ParentName) + "(" + getBasename(File->getName()) +
+          ")")
 }

test/COFF/filename-casing.s

+# REQUIRES: x86
+
+# RUN: llvm-mc -filetype=obj -triple=x86_64-windows-msvc -o %T/MixedCase.obj %s
+# RUN: not lld-link /entry:main %T/MixedCase.obj 2>&1 | FileCheck -check-prefix=OBJECT %s
+
+# RUN: llvm-lib /out:%T/MixedCase.lib %T/MixedCase.obj
+# RUN: not lld-link /machine:x64 /entry:main %T/MixedCase.lib 2>&1 | FileCheck -check-prefix=ARCHIVE %s
+
+# OBJECT: MixedCase.obj: undefined symbol: f
+# ARCHIVE: MixedCase.lib(MixedCase.obj): undefined symbol: f
+
+.globl main
+main:
+  callq f