and split it out of -Wgnu into its own warning flag.
* In C++11, this is now a hard error (GCC has no extension here in C++11 mode).
The error can be disabled with -Wno-static-float-init, and has a fixit to
add 'constexpr'.
* In C++98, this is still an ExtWarn, but is now controlled by
-Wstatic-float-init as well as -Wgnu.
llvm-svn: 173414