fix: added missing subsitution in build.sh

Author: zaucy

build.sh

@@ -154,6 +154,7 @@ if [ -f "$ROOT_DIR/.cache/cpp2/source/_build/cpp2b.cppm" ]; then
 fi
 
 cat "$ROOT_DIR/share/cpp2b.cppm.tpl" | sed "s\`@CPP2B_PROJECT_ROOT@\`$ROOT_DIR\`g" > "$ROOT_DIR/.cache/cpp2/source/_build/cpp2b.cppm"
+cat "$ROOT_DIR/share/cpp2b.cppm.tpl" | sed "s\`@CPP2B_COMPILER@\`clang\`g" > "$ROOT_DIR/.cache/cpp2/source/_build/cpp2b.cppm"
 
 $CPP2B_COMPILER                                       \
     -stdlib=libc++                                    \