[lldb] Fix interpreting absolute Windows paths with forward slashes

[mstorsjo]

Summary

In practice, Windows paths can use either backslashes or forward slashes.

This fixes an issue reported downstream at
https://github.com/mstorsjo/llvm-mingw/issues/266.

lldb/source/Plugins/SymbolFile/DWARF/DWARFUnit.cpp

removeHostnameFromPathname(llvm::StringRef path_from_dwarf) {
   llvm::StringRef host, path;
   std::tie(host, path) = path_from_dwarf.split(':');
 
   if (host.contains('/'))
     return path_from_dwarf;
 
   // check whether we have a windows path, and so the first character is a
   // drive-letter not a hostname.
-  if (host.size() == 1 && llvm::isAlpha(host[0]) && path.startswith("\\"))
+  if (host.size() == 1 && llvm::isAlpha(host[0]) &&
+      (path.startswith("\\") || path.startswith("/")))
     return path_from_dwarf;
 
   return path;
 }
 
 void DWARFUnit::ComputeCompDirAndGuessPathStyle() {
   m_comp_dir = FileSpec();
   const DWARFDebugInfoEntry *die = GetUnitDIEPtrOnly();

lldb/source/Utility/FileSpec.cpp

 }
 
 llvm::Optional<FileSpec::Style> FileSpec::GuessPathStyle(llvm::StringRef absolute_path) {
   if (absolute_path.startswith("/"))
     return Style::posix;
   if (absolute_path.startswith(R"(\\)"))
     return Style::windows;
   if (absolute_path.size() >= 3 && llvm::isAlpha(absolute_path[0]) &&
-      absolute_path.substr(1, 2) == R"(:\)")
+      (absolute_path.substr(1, 2) == R"(:\)" ||
+       absolute_path.substr(1, 2) == R"(:/)"))
     return Style::windows;
   return llvm::None;
 }
 
 // Dump the object to the supplied stream. If the object contains a valid
 // directory name, it will be displayed followed by a directory delimiter, and
 // the filename.
 void FileSpec::Dump(llvm::raw_ostream &s) const {

lldb/unittests/Utility/FileSpecTest.cpp

 }
 
 TEST(FileSpecTest, GuessPathStyle) {
   EXPECT_EQ(FileSpec::Style::posix, FileSpec::GuessPathStyle("/foo/bar.txt"));
   EXPECT_EQ(FileSpec::Style::posix, FileSpec::GuessPathStyle("//net/bar.txt"));
   EXPECT_EQ(FileSpec::Style::windows,
             FileSpec::GuessPathStyle(R"(C:\foo.txt)"));
   EXPECT_EQ(FileSpec::Style::windows,
+            FileSpec::GuessPathStyle(R"(C:/foo.txt)"));
+  EXPECT_EQ(FileSpec::Style::windows,
             FileSpec::GuessPathStyle(R"(\\net\foo.txt)"));
   EXPECT_EQ(FileSpec::Style::windows, FileSpec::GuessPathStyle(R"(Z:\)"));
+  EXPECT_EQ(FileSpec::Style::windows, FileSpec::GuessPathStyle(R"(Z:/)"));
   EXPECT_EQ(llvm::None, FileSpec::GuessPathStyle("foo.txt"));
   EXPECT_EQ(llvm::None, FileSpec::GuessPathStyle("foo/bar.txt"));
   EXPECT_EQ(llvm::None, FileSpec::GuessPathStyle("Z:"));
 }
 
 TEST(FileSpecTest, GetPath) {
   std::pair<const char *, const char *> posix_tests[] = {
       {"/foo/.././bar", "/bar"},