build: make the c-api CMakeLists.txt easier to import (#8496)

Currently the CMakeLists.txt is designed to only be consumed by a parent
project, which limits its flexibility. Adding a `project()` function
allows it to also be built as its own project.

Also set `USES_TERMINAL_BUILD` to `TRUE` in `ExternalProject_Add()`,
which allows getting the installation progress output from `cargo
build`.

crates/c-api/CMakeLists.txt

@@ -1,4 +1,5 @@
 cmake_minimum_required(VERSION 3.10)
+project(wasmtime C)
 
 set(WASMTIME_USER_CARGO_BUILD_OPTIONS "" CACHE STRING "Additional cargo flags (such as --features) to apply to the build command")
 option(BUILD_SHARED_LIBS "Build using shared libraries" OFF)
@@ -83,6 +84,7 @@ ExternalProject_Add(
 	CONFIGURE_COMMAND ""
 	INSTALL_COMMAND "${WASMTIME_INSTALL_COMMAND}"
         BUILD_COMMAND ${WASMTIME_PREBUILD_COMMAND} ${WASMTIME_CARGO_BINARY} build ${WASMTIME_BUILD_TYPE_FLAG} ${WASMTIME_USER_CARGO_BUILD_OPTIONS} ${WASMTIME_BUILD_TARGET}
+	USES_TERMINAL_BUILD TRUE
 	BINARY_DIR ${CMAKE_CURRENT_SOURCE_DIR}/artifact
         BUILD_ALWAYS ${WASMTIME_ALWAYS_BUILD}
 	BUILD_BYPRODUCTS ${WASMTIME_BUILD_PRODUCT})