Improve Emscripten detection.

__EMSCRIPTEN_major__ is only guaranteed to be defined if
the program #includes "emscripten/version.h", but
__EMSCRIPTEN__ should always be defined:

https://emscripten.org/docs/compiling/Building-Projects.html#detecting-emscripten-in-preprocessor

Bug: b/305974160
Change-Id: I831620d50a216850b175f6f6f25988f25355e06f
Reviewed-on: https://skia-review.googlesource.com/c/skcms/+/782438
Commit-Queue: Brian Osman <brianosman@google.com>
Auto-Submit: John Stiles <johnstiles@google.com>
Reviewed-by: Brian Osman <brianosman@google.com>
1 file changed