fix(build): name the compiler the check requires, and the option that failed (#18594)

build.sh

@@ -503,7 +503,7 @@ Build script for RAGFlow Go server with C++ bindings.
 OPTIONS:
     --all, -a       Build everything (C++ library + Go server) [default]
     --cpp, -c       Build only C++ static library
-    --cpp-test      Build C++ test executable (requires --cpp first)
+    --cpp-test      Build C++ test executable (builds the C++ library if needed)
     --go, -g        Build only Go server (requires C++ library to be built)
     --test, -t      Run Go unit tests (no build tag). Sets up the CGO env and
                     native static libs (office_oxide/pdfium/pdf_oxide) needed to
@@ -539,8 +539,8 @@ EXAMPLES:
 
 DEPENDENCIES:
     - cmake >= 4.0
-    - go >= 1.24
-    - g++ with C++17/23 support
+    - go >= 1.26.4
+    - clang++ with C++20 support
     - office_oxide native library (download with: uv run python3 ragflow_deps/download_go_deps.py)
     - lld (Linux only): sudo apt install lld-20 && sudo ln -s /usr/bin/ld.lld-20 /usr/bin/ld.lld
     - pcre2 development files
@@ -636,7 +636,7 @@ main() {
             echo "Binary: $RAGFLOW_SERVER_BINARY, $RAGFLOW_CLI_BINARY"
             ;;
         *)
-            echo -e "${RED}Unknown option: $1${NC}"
+            echo -e "${RED}Unknown option: ${args[0]}${NC}"
             show_help
             exit 1
             ;;