* Removing pragma for GCC -Wattributes, fixing forward declarations.

* Introducing PYBIND11_NOINLINE_FWD to deal with CUDA, GCC7, GCC8.

* Updating PYBIND11_NOINLINE_DCL in Doxyfile.

* Trying noinline, noinline for {CUDA, GCC7, GCC8}

* Trying noinline, inline for {CUDA, GCC7, GCC8}

* Adding GCC -Wattributes `pragma` in 3 header files.

* Introducing PYBIND11_NOINLINE_GCC_PRAGMA_ATTRIBUTES_NEEDED, used in 9 header files.

* Removing ICC pragma 2196, to see if it is still needed.

* Trying noinline, noinline for ICC

* Trying noinline, inline for ICC

* Restoring ICC pragma 2196, introducing PYBIND11_NOINLINE_FORCED, defined for testing.

* Removing code accidentally left in (was for experimentation only).

* Removing one-time-test define.

* Removing PYBIND11_NOINLINE_FWD macro (after learning that it makes no sense).

* Testing with PYBIND11_NOINLINE_DISABLED. Minor non-functional enhancements.

* Removing #define PYBIND11_NOINLINE_DISABLED (test was successful).

* Removing PYBIND11_NOINLINE_FORCED and enhancing comments for PYBIND11_NOINLINE.

* WIP stripping back

* Making -Wattributes pragma in pybind11 specific to GCC7, GCC8, CUDA.