Revert "WASM build: disable legacy exception handling."

This reverts commit 49853607e6.

The option `-wasm-use-legacy-eh=false` does not seem to be
recognized in the version of the compiler we are now using.

Reopens #11787.

cabal.project

@@ -28,7 +28,6 @@ if arch(wasm32)
   package lua
     flags: +cross-compile
     ghc-options: -optc-mllvm
-                 -optc-wasm-use-legacy-eh=false
                  -optc-wasm-enable-sjlj
                  -optc-D_WASI_EMULATED_PROCESS_CLOCKS
                  -optc-D_WASI_EMULATED_SIGNAL