Avoid using C++14 to build CMake if cstdio breaks

The GNU 4.8 standard library's cstdio header is not aware that C++14
honors C11's removal of "gets" from stdio.h and results in an error:

  /.../include/c++/4.8/cstdio:120:11: error: no member named 'gets' in the global namespace

Detect this problematic case and default to using C++11 instead of
C++14 for building CMake itself.

1 files changed, 2 insertions, 0 deletions

diff --git a/Source/Checks/cm_cxx14_cstdio.cpp b/Source/Checks/cm_cxx14_cstdio.cpp
new file mode 100644
index 0000000..3a6a699
--- /dev/null
+++ b/Source/Checks/cm_cxx14_cstdio.cpp
@@ -0,0 +1,2 @@
+#include <cstdio>
+int main() { return 0; }