Fixes to enable building for Wasm targets #150

Job	Run time
Rust builds (using Delta extension) / Generate matrix	3s
Extension template / Generate matrix	4s
Extension template / DuckDB-Wasm (wasm_mvp, wasm32-emscripten)	3m 28s
Extension template / Linux (linux_amd64, ubuntu:18.04, x64-linux)	6m 41s
Extension template / DuckDB-Wasm (wasm_eh, wasm32-emscripten)	3m 29s
Extension template / Linux (linux_amd64_gcc4, quay.io/pypa/manylinux2014_x86_64, x64-linux)	6m 1s
Extension template / DuckDB-Wasm (wasm_threads, wasm32-emscripten)	3m 29s
Extension template / Linux (linux_arm64, ubuntu:18.04, arm64-linux)	7m 36s
Extension template / Windows (windows_amd64, x64-windows-static-md)	22m 3s
Extension template / MacOS (osx_amd64, x86_64, x64-osx)	3m 7s
Extension template / Windows (windows_amd64_rtools, x64-mingw-static)	45m 13s
Extension template / MacOS (osx_arm64, arm64, arm64-osx)	2m 4s
Rust builds (using Delta extension) / MacOS (osx_amd64, x86_64, x64-osx)	8m 26s
Rust builds (using Delta extension) / DuckDB-Wasm	0s
Rust builds (using Delta extension) / Linux (linux_amd64, ubuntu:18.04, x64-linux)	19m 17s
Rust builds (using Delta extension) / MacOS (osx_arm64, arm64, arm64-osx)	7m 57s
Rust builds (using Delta extension) / Linux (linux_amd64_gcc4, quay.io/pypa/manylinux2014_x86_64, x64-linux)	19m 46s
Rust builds (using Delta extension) / Linux (linux_arm64, ubuntu:18.04, arm64-linux)	21m 43s
Rust builds (using Delta extension) / Windows	0s
	3h 0m 27s

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