This patch modifies the CMakeLists.txt file and a few sources
in order to build the SwiftShader Vulkan ICD for Fuchsia with
CMake.

Note that building EGL/GLES_CM/GLESv2 and tests is not supported,
and should be explicitly disabled when configuring the build,
e.g.:

  mkdir build-fuchsia && build-fuchsia
  cmake .. \
    -DCMAKE_TOOLCHAIN_FILE=.../FuchsiaSdkToolchain.cmake \
    -DCMAKE_BUILD_TYPE=Release \
    -DSWIFTSHADER_BUILD_TESTS=0 \
    -DSWIFTSHADER_BUILD_EGL=0 \
    -DSWIFTSHADER_BUILD_GLES_CM=0 \
    -DSWIFTSHADER_BUILD_GLESv2=0 \
    <other-cmake-options>

  make  # or ninja

NOTE: This should not affect the build for other platforms!

This will make it easier to conditionally add Fuchsia-specific
sources to the build (see discussion on b/144687651 for details).

The BUILD.gn file will still be maintained in parallel for
Fuchsia-specific changes.

NOTE: As of now, the Fuchsia SDK doesn't provide a way for
      third-party code to access the framebuffer directly.

      Instead, client code should rely on Vulkan presentation
      surfaces or higher-level APIs provided by the compositor
      that are still in flux / unstable. Hence this will appear
      in a future CL.

Bug: b/143122483
Bug: b/144687651
Change-Id: Ica3b98f5a8eb1370287e2bb4ff22ef938aaa4b49
Reviewed-on: https://swiftshader-review.googlesource.com/c/SwiftShader/+/38488Reviewed-by: Nicolas Capens <nicolascapens@google.com>
Kokoro-Result: kokoro <noreply+kokoro@google.com>
Tested-by: David Turner <digit@google.com>