Features: Enable compiler extensions by default.

Compilers enable their extensions by default, and disabling them
implicitly can lead to results which are surprising or non-obvious
to debug.

 http://public.kitware.com/pipermail/cmake-developers/2014-May/010575.html
 http://thread.gmane.org/gmane.comp.programming.tools.cmake.devel/10214
 https://www.mail-archive.com/cmake-developers@cmake.org/msg10116.html
 (Compiler feature extensions by default, 29 May 2014)

4 files changed, 10 insertions, 8 deletions

diff --git a/Help/prop_tgt/CXX_EXTENSIONS.rst b/Help/prop_tgt/CXX_EXTENSIONS.rst
index d7f87a4..67c5cb0 100644
--- a/Help/prop_tgt/CXX_EXTENSIONS.rst
+++ b/Help/prop_tgt/CXX_EXTENSIONS.rst
@@ -5,7 +5,8 @@ Boolean specifying whether compiler specific extensions are requested.
 
 This property specifies whether compiler specific extensions should be
 used.  For some compilers, this results in adding a flag such
-as ``-std=gnu++11`` instead of ``-std=c++11`` to the compile line.
+as ``-std=gnu++11`` instead of ``-std=c++11`` to the compile line.  This
+property is ``ON`` by default.
 
 See the :manual:`cmake-compile-features(7)` manual for information on
 compile features.
diff --git a/Help/prop_tgt/CXX_STANDARD.rst b/Help/prop_tgt/CXX_STANDARD.rst
index 8f299bb..b50cdf9 100644
--- a/Help/prop_tgt/CXX_STANDARD.rst
+++ b/Help/prop_tgt/CXX_STANDARD.rst
@@ -5,7 +5,7 @@ The C++ standard whose features are requested to build this target.
 
 This property specifies the C++ standard whose features are requested
 to build this target.  For some compilers, this results in adding a
-flag such as ``-std=c++11`` to the compile line.
+flag such as ``-std=gnu++11`` to the compile line.
 
 Supported values are ``98`` and ``11``.
 
@@ -17,9 +17,9 @@ means that using:
 
   set_property(TARGET tgt PROPERTY CXX_STANDARD 11)
 
-with a compiler which does not support ``-std=c++11`` or an equivalent
+with a compiler which does not support ``-std=gnu++11`` or an equivalent
 flag will not result in an error or warning, but will instead add the
-``-std=c++98`` flag if supported.  This "decay" behavior may be controlled
+``-std=gnu++98`` flag if supported.  This "decay" behavior may be controlled
 with the :prop_tgt:`CXX_STANDARD_REQUIRED` target property.
 
 See the :manual:`cmake-compile-features(7)` manual for information on
diff --git a/Help/prop_tgt/C_EXTENSIONS.rst b/Help/prop_tgt/C_EXTENSIONS.rst
index 0772ecc..dc48cc6 100644
--- a/Help/prop_tgt/C_EXTENSIONS.rst
+++ b/Help/prop_tgt/C_EXTENSIONS.rst
@@ -5,7 +5,8 @@ Boolean specifying whether compiler specific extensions are requested.
 
 This property specifies whether compiler specific extensions should be
 used.  For some compilers, this results in adding a flag such
-as ``-std=gnu11`` instead of ``-std=c11`` to the compile line.
+as ``-std=gnu11`` instead of ``-std=c11`` to the compile line.  This
+property is ``ON`` by default.
 
 See the :manual:`cmake-compile-features(7)` manual for information on
 compile features.
diff --git a/Help/prop_tgt/C_STANDARD.rst b/Help/prop_tgt/C_STANDARD.rst
index a0c939a..88ca926 100644
--- a/Help/prop_tgt/C_STANDARD.rst
+++ b/Help/prop_tgt/C_STANDARD.rst
@@ -5,7 +5,7 @@ The C standard whose features are requested to build this target.
 
 This property specifies the C standard whose features are requested
 to build this target.  For some compilers, this results in adding a
-flag such as ``-std=c11`` to the compile line.
+flag such as ``-std=gnu11`` to the compile line.
 
 Supported values are ``90``, ``99`` and ``11``.
 
@@ -17,9 +17,9 @@ means that using:
 
   set_property(TARGET tgt PROPERTY C_STANDARD 11)
 
-with a compiler which does not support ``-std=c11`` or an equivalent
+with a compiler which does not support ``-std=gnu11`` or an equivalent
 flag will not result in an error or warning, but will instead add the
-``-std=c99`` or ``-std=c90`` flag if supported.  This "decay" behavior may
+``-std=gnu99`` or ``-std=gnu90`` flag if supported.  This "decay" behavior may
 be controlled with the :prop_tgt:`C_STANDARD_REQUIRED` target property.
 
 See the :manual:`cmake-compile-features(7)` manual for information on