wasm: only export explicitly exported functions

Previously we used the --export-all linker flag to export most
functions. However, this is not needed and possibly increases binary
size. Instead, we should be exporting the specific functions to be
exported.

targets/wasm.json

@@ -14,7 +14,6 @@
 	"ldflags": [
 		"--allow-undefined",
 		"--stack-first",
-		"--export-all",
 		"--no-demangle"
 	],
 	"emulator":      ["node", "targets/wasm_exec.js"],