Chromium will want to have both static and shared library versions of
Dawn to use in non-component and component builds respectively.
The *_export.h files are modified to noop when *_SHARED_LIBRARY is not
defined so that the static library doesn't export symbols that aren't
imported in dependents (this would break compilation on Windows).
A dawn_library_combo is introduced in BUILD.gn that factors out all the
logic needed to produce shared libraries and handle the _EXPORT macros.
Also contains a fix to dawncpp to export only the methods that aren't
defined in the header (otherwise they get defined multiple times)
BUG=dawn:85
Change-Id: Ib747deb9308e1165dd66002487147ba279d3eac0
Reviewed-on: https://dawn-review.googlesource.com/c/3761
Reviewed-by: Corentin Wallez <cwallez@chromium.org>
Commit-Queue: Corentin Wallez <cwallez@chromium.org>
WIN32 is defined by the SDK, but _WIN32 is defined by the compiler.
Since Dawn doesn't necessarily include <windows.h> everywhere dawn.h is
included, we should use _WIN32 (which will always be defined).
