Fix Features of wabt.post.js can't work in strict mode

[Changqing-JING]

for ([f, v] of Object.entries(FEATURES)) leads to ReferenceError: f is not defined in use strict.
Fix it

[sbc100]

Should we add -sSTRICT (or just -sSTRICT_JS) to the build flags to wabt.js maybe?

[Changqing-JING]

@sbc100
Thank you very much for review. -sSTRICT_JS can't be set, because:
The current CMakeLists has already set -s MODULARIZE=1, which is conflict with -sSTRICT_JS.
If -sSTRICT_JS is set, it will lead to error:
em++: error: STRICT_JS doesn't work with MODULARIZE or EXPORT_ES6

[Changqing-JING]

@sbc100 can this PR be merged? The bug is blocking our esbuild pack