Disable name mangling for the component type object link symbol, and ensure it isn't discarded by the linker (#1326)

Author: TartanLlama

crates/c/src/lib.rs

@@ -316,6 +316,7 @@ impl WorldGenerator for C {
             self.src.c_adapters,
             "
                extern void {linking_symbol}(void);
+               __attribute__((used))
                void {linking_symbol}_public_use_in_this_compilation_unit(void) {{
                    {linking_symbol}();
                }}

crates/cpp/src/lib.rs

@@ -654,7 +654,8 @@ impl WorldGenerator for Cpp {
         uwrite!(
             c_str.src,
             "#ifdef __wasm32__
-                   extern void {linking_symbol}(void);
+                   extern \"C\" void {linking_symbol}(void);
+                   __attribute__((used))
                    void {linking_symbol}_public_use_in_this_compilation_unit(void) {{
                        {linking_symbol}();
                    }}