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, 2 insertions, 2 deletions

diff --git a/src/buildtool/logging/log_level.hpp b/src/buildtool/logging/log_level.hpp
index 1902e960..bbc599b9 100644
--- a/src/buildtool/logging/log_level.hpp
+++ b/src/buildtool/logging/log_level.hpp
@@ -20,7 +20,7 @@
 #include <string>
 #include <type_traits>
 
-#include <gsl-lite/gsl-lite.hpp>
+#include <gsl/gsl>
 
 enum class LogLevel {
     Error,    ///< Error messages, fatal errors
@@ -76,7 +76,7 @@ constexpr auto kLastLogLevel = LogLevel::Trace;
         case LogLevel::Trace:
             return "TRACE";
     }
-    gsl_Ensures(false);  // unreachable
+    Ensures(false);  // unreachable
 }
 
 #endif  // INCLUDED_SRC_BUILDTOOL_LOGGING_LOG_LEVEL_HPP