RETAIN_COMPILER_SETTINGS, Runtime.getCompilerSetting and emscripten_get_compiler_setting - an optional way to look up compiler flags at runtime
optimize traverseGenerated
tolerate non-asm variables in asm optimization passes, with no-op coercions (x=x)
support memory growth in (non-validating) asm.js
Merge remote-tracking branch 'upstream/incoming' into incoming