imports: Switch to Microsoft GSL implementation

... with two minor code base changes compared to previous
use of gsl-lite:

- dag.hpp: ActionNode::Ptr and ArtifactNode::Ptr are not
  wrapped in gsl::not_null<> anymore, due to lack of support
  for wrapping std::unique_ptr<>. More specifically, the
  move constructor is missing, rendering it impossible to
  use std::vector<>::emplace_back().

- utils/cpp/gsl.hpp: New header file added to implement the
  macros ExpectsAudit() and EnsureAudit(), asserts running
  only in debug builds, which were available in gsl-lite but
  are missing in MS GSL.

1 files changed, 1 insertions, 1 deletions

diff --git a/src/buildtool/main/main.cpp b/src/buildtool/main/main.cpp
index b6796c05..81a932a1 100644
--- a/src/buildtool/main/main.cpp
+++ b/src/buildtool/main/main.cpp
@@ -449,7 +449,7 @@ void SetupHashFunction() {
                             FileRoot const& root,
                             std::vector<std::string> const& markers)
     -> std::optional<std::filesystem::path> {
-    gsl_Expects(subdir.is_relative());
+    Expects(subdir.is_relative());
     auto current = subdir;
     while (true) {
         for (auto const& marker : markers) {