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, 4 insertions, 0 deletions

diff --git a/configure.py b/configure.py
index 4390434..99a2c86 100755
--- a/configure.py
+++ b/configure.py
@@ -305,6 +305,8 @@ if platform.is_msvc():
 else:
     n.variable('ar', configure_env.get('AR', 'ar'))
 
+# Note that build settings are separately specified in CMakeLists.txt and
+# these lists should be kept in sync.
 if platform.is_msvc():
     cflags = ['/showIncludes',
               '/nologo',  # Don't print startup banner.
@@ -320,6 +322,7 @@ if platform.is_msvc():
               # Disable warnings about ignored typedef in DbgHelp.h
               '/wd4091',
               '/GR-',  # Disable RTTI.
+              '/Zc:__cplusplus',
               # Disable size_t -> int truncation warning.
               # We never have strings or arrays larger than 2**31.
               '/wd4267',
@@ -339,6 +342,7 @@ else:
               '-Wno-unused-parameter',
               '-fno-rtti',
               '-fno-exceptions',
+              '-std=c++11',
               '-fvisibility=hidden', '-pipe',
               '-DNINJA_PYTHON="%s"' % options.with_python]
     if options.debug: