fix compilation for target wasm32-wasi

[wasm-forge]

This PR partially reverts #961 that has introduced a bug in detection of wasm32-wasi target. That PR replaced the check of TARGET with a check of CARGO_CFG_TARGET_ENV. That however is incorrect because wasm32-wasi is a CPU architecture target (similar to x86 and armv8) and not an operating system.

This PR only affects wasm32-wasi compilation and is a no-op for other targets.

[gwenn]

See #1116 and #1289

[wasm-forge]

@gwenn, thanks for the reply and linking the existing attempts to fix the bug. I apologize for sending a PR with an empty description. I fixed it now.

The bug was introduced in 5511a12?diff=split#diff-c1c013e096409a5aea1f123c04254379057791785963eba5ef253fdd686570b8L120

My PR reverts the change that introduced the bug. I verified locally that wasm32-wasi works locally after this partial revert.

My fix looks very similar to PR #1116, but it doesn't have the || is_compiler(..) part which is superfluous. If you would like to proceed with PR #1116, I am happy to close my PR and continue the work in #1116.

The PR #1289 is incorrect because it is changing the definition of is_compiler().

[gwenn]

Thanks for the explanation.

[codecov]

Codecov Report

Patch coverage: 100.00% and no project coverage change.

Comparison is base (051dcf6) 80.48% compared to head (ef4a0ac) 80.48%.

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #1321   +/-   ##
=======================================
  Coverage   80.48%   80.48%           
=======================================
  Files          49       49           
  Lines        9946     9946           
=======================================
  Hits         8005     8005           
  Misses       1941     1941           

Impacted Files	Coverage Δ
libsqlite3-sys/build.rs	64.57% <100.00%> (ø)

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