Build ninja with C++11 (#2089)

* Build ninja with C++11

In order to allow future use of std::chrono to make the stats code
portable it is desirable to compile with C++11. Doing so also allows use
of std::unordered_map, and reduces the number of #ifdefs in the ninja
source code.

Switching to C++11 requires modifying both CMakeLists.txt and
configure.py, for MSVC and for other build systems. For MSVC the
required change is adding /Zc:__cplusplus to tell the compiler to
give a more accurate value for the __cplusplus macro. For other
platforms the change is to add -std=c++11 or the CMake equivalent.

This change makes some progress towards resolving issue #2004.

* Delete code and instructions

C++11 guarantees that string::data() gives null-terminated pointers, so
explicitly adding a null terminator is no longer needed.

The Google C++ Style Guide already recommends avoiding unnecessary use
of C++14 and C++17 so repeating this in CONTRIBUTING.md is not critical.

These changes both came from PR-review suggestions.

* Only set cxx_std_11 if standard is 98

* Return to unconditional target_compile_features use

After much discussion it sounds like using target_compile_features
unconditionally is best.

1 files changed, 0 insertions, 7 deletions

diff --git a/src/missing_deps.h b/src/missing_deps.h
index ae57074..7a615da 100644
--- a/src/missing_deps.h
+++ b/src/missing_deps.h
@@ -19,9 +19,7 @@
 #include <set>
 #include <string>
 
-#if __cplusplus >= 201103L
 #include <unordered_map>
-#endif
 
 struct DepsLog;
 struct DiskInterface;
@@ -68,13 +66,8 @@ struct MissingDependencyScanner {
   int missing_dep_path_count_;
 
  private:
-#if __cplusplus >= 201103L
   using InnerAdjacencyMap = std::unordered_map<Edge*, bool>;
   using AdjacencyMap = std::unordered_map<Edge*, InnerAdjacencyMap>;
-#else
-  typedef std::map<Edge*, bool> InnerAdjacencyMap;
-  typedef std::map<Edge*, InnerAdjacencyMap> AdjacencyMap;
-#endif
   AdjacencyMap adjacency_map_;
 };