cmake: Test each compiler flag

Add non-trival C compiler flags only if check_c_compiler_flag()
succeeds.

This fixes the build with 4.8.1, which was broken by

 commit cbab09dc0e6eb8fcea40db92319305d5e136d4b9
 cmake: Compile with stricter error checking

 Add -Werror=incompatible-pointer-types and -Werror=int-conversion
 to the compiler flags.

Signed-off-by: Chad Versace <chad.versace@linux.intel.com>
android: Fix build by defining WAFFLE_API_VERSION

Oops. I broke the Android build in commit d4728dd "waffle: Add feature test
macro WAFFLE_API_VERSION". Fix it by defining WAFFLE_API_VERSION=0x0103.

Actually... I *hope* that this fixes the build. I no longer have an Android
tree to test with.

Signed-off-by: Chad Versace <chad.versace@linux.intel.com>
man: Add feature macro WAFFLE_API_EXPERIMENTAL

waffle_window_resize() is proving difficult to implement because Waffle
lacks an event model.  We need a way to prevent clients from
accidentally using it, on the master branch as well in stable releases,
until it gets fixed or removed.

All future API additions that I have strong doubts about will get
guarded by WAFFLE_API_EXPERIMENTAL.

Signed-off-by: Chad Versace <chad.versace@linux.intel.com>
cmake,android: Define WAFFLE_API_EXPERIMENTAL

This is required before actually marking any API as experimental to
prevent the build from breaking.

Signed-off-by: Chad Versace <chad.versace@linux.intel.com>
waffle: Mark waffle_window_resize() as experimental

That is, guard it with the feature macro WAFFLE_API_EXPERIMENTAL.

waffle_window_resize() is proving to dificult to implement because
Waffle lacks an event model.

It seems to work properly on Wayland. It works on CGL but the resize is
janky. It kinda works on composited X11 but interacts badly with GL
rendering; the client needs to stall after resize to provide the
compositor sufficient time to process the request before the client
begins to draw... ouch. I haven't tested it on Android.

So... until waffle_window_resize() actually works it needs to remain
experimental until we do one of:

    1. Make it synchronous on all platforms. (I'm having difficulty
       doing this on composited X11).

    2. Waffle exposes API for an event model, into which window resizes
       are integrated. (This is likely the wrong direction).

    3. We kill waffle_window_resize().

CC: Juha-Pekka Heikkila <juha-pekka.heikkila@linux.intel.com>
Signed-off-by: Chad Versace <chad.versace@linux.intel.com>
doc: Add preliminary waffle-1.3.0 release notes

Signed-off-by: Chad Versace <chad.versace@linux.intel.com>