Features: Add cxx_constexpr.

Help/variable/CMAKE_CXX_KNOWN_FEATURES.rst

@@ -17,6 +17,11 @@ The features known to this version of CMake are:
 
   .. _N1984: http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2006/n1984.pdf
 
+``cxx_constexpr``
+  Constant expressions, as defined in N2235_.
+
+  .. _N2235: http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2007/n2235.pdf
+
 ``cxx_delegating_constructors``
   Delegating constructors, as defined in N1986_.
 

Modules/Compiler/GNU-CXX-FeatureTests.cmake

@@ -10,6 +10,9 @@ set(_cmake_feature_test_cxx_delegating_constructors "${GNU47_CXX11}")
 # support -std=c++11. Prior to that, support for C++11 features is technically
 # experiemental and possibly incomplete (see for example the note below about
 # cxx_variadic_template_template_parameters)
+# TODO: Should be supported by GNU 4.6
+set(GNU46_CXX11 "${_oldestSupported} && __cplusplus >= 201103L")
+set(_cmake_feature_test_cxx_constexpr "${GNU46_CXX11}")
 # TODO: Should be supported by GNU 4.4
 set(GNU44_CXX11 "${_oldestSupported} && __cplusplus >= 201103L")
 set(_cmake_feature_test_cxx_auto_type "${GNU44_CXX11}")

Source/cmMakefile.cxx

@@ -43,6 +43,7 @@
 
 #define FOR_EACH_CXX_FEATURE(F) \
   F(cxx_auto_type) \
+  F(cxx_constexpr) \
   F(cxx_delegating_constructors) \
   F(cxx_variadic_templates)
 

Tests/CompileFeatures/cxx_constexpr.cpp

@@ -0,0 +1,5 @@
+
+constexpr int getNum()
+{
+  return 42;
+}