[docs] Add BE debug build instruction to docs (#21964)

docs/en/docs/install/source-install/compilation-general.md

@@ -142,6 +142,12 @@ This topic is about how to compile Doris from source.
     $ sh build.sh
     ```
 
+   To build debug version for BE, add BUILD_TYPE=Debug.
+
+    ```
+    $ BUILD_TYPE=Debug sh build.sh
+    ```
+
    After compilation, the output files will be in the `output/` directory.
 
     > **Note:**
@@ -215,6 +221,12 @@ You can compile Doris directly in your own Linux environment.
     $ USE_AVX2=0 sh build.sh
     ```
 
+   To build debug version for BE, add BUILD_TYPE=Debug.
+
+    ```
+    $ BUILD_TYPE=Debug sh build.sh
+    ```
+
    After compilation, the output files will be in the `output/` directory.
 
 ## FAQ

docs/en/docs/install/source-install/compilation-with-ldb-toolchain.md

@@ -125,6 +125,11 @@ $ USE_AVX2=0 sh build.sh
 
 If supported, execute `sh build.sh` directly.
 
+To build debug version for BE, add BUILD_TYPE=Debug.
+```
+$ BUILD_TYPE=Debug sh build.sh
+```
+
 This script will compile the third-party libraries first and then the Doris components (FE, BE) later. The compiled output will be in the `output/` directory.
 
 ## Precompile the Third-Party Binaries

docs/zh-CN/docs/install/source-install/compilation-general.md

@@ -140,7 +140,12 @@ under the License.
    ```
    $ sh build.sh
    ```
-   
+
+   如需编译Debug版本的BE，增加 BUILD_TYPE=Debug
+   ```
+   $ BUILD_TYPE=Debug sh build.sh
+   ```
+
    编译完成后，产出文件在 `output/` 目录中。
    
    >**注意:**
@@ -208,7 +213,12 @@ under the License.
    ```
    $ USE_AVX2=0 sh build.sh
    ```
-   
+
+   如需编译Debug版本的BE，增加 BUILD_TYPE=Debug
+   ```
+   $ BUILD_TYPE=Debug sh build.sh
+   ```
+
    编译完成后，产出文件在 `output/` 目录中。
 
 ## 常见问题

docs/zh-CN/docs/install/source-install/compilation-with-ldb-toolchain.md

@@ -125,6 +125,11 @@ $ USE_AVX2=0 sh build.sh
 
 若支持则直接执行 `sh build.sh` 即可
 
+如需编译Debug版本的BE，增加 BUILD_TYPE=Debug
+```
+$ BUILD_TYPE=Debug sh build.sh
+```
+
 该脚本会先编译第三方库，之后再编译 Doris 组件（FE、BE）。编译产出在 `output/` 目录下。
 
 ## 预编译三方库