Docker: Genericise MODULE_PREBUILD_wasm for re-use

Rename this variable to MODULE_PREBUILD_wasm_common so it can be used by
both the existing wasm dockerfile and a new wasm-wasi-component
dockerfile.

Signed-off-by: Andrew Clayton <[email protected]>

Author: ac000

pkg/docker/Makefile

@@ -80,7 +80,9 @@ CONTAINER_wasm ?= debian:$(VARIANT)-slim
 CONFIGURE_wasm ?= wasm --include-path=\`pwd\`/pkg/contrib/wasmtime/crates/c-api/include --lib-path=/usr/lib/\$$(dpkg-architecture -q DEB_HOST_MULTIARCH)/
 INSTALL_wasm ?=	wasm-install
 RUN_wasm ?=		/bin/true
-define MODULE_PREBUILD_wasm
+MODULE_PREBUILD_wasm ?= $(MODULE_PREBUILD_wasm_common)
+
+define MODULE_PREBUILD_wasm_common
 export RUST_VERSION=1.71.0 \\\n \
 \ \ \ \&\& export RUSTUP_HOME=/usr/src/unit/rustup \\\n \
 \ \ \ \&\& export CARGO_HOME=/usr/src/unit/cargo \\\n    \