Get gcc version by script to support cross-compile (#2567)

Fix #1631

Author: wasphin

config_brpc.sh

@@ -89,7 +89,7 @@ elif [ -z "$CXX" ]; then
     exit 1
 fi
 
-GCC_VERSION=$($CXX tools/print_gcc_version.cc -o print_gcc_version && ./print_gcc_version && rm ./print_gcc_version)
+GCC_VERSION=$(CXX=$CXX tools/print_gcc_version.sh)
 if [ $GCC_VERSION -gt 0 ] && [ $GCC_VERSION -lt 40800 ]; then
     >&2 $ECHO "GCC is too old, please install a newer version supporting C++11"
     exit 1

tools/print_gcc_version.cc

@@ -0,0 +1,41 @@
+#!/usr/bin/env bash
+
+# Licensed to the Apache Software Foundation (ASF) under one or more
+# contributor license agreements.  See the NOTICE file distributed with
+# this work for additional information regarding copyright ownership.
+# The ASF licenses this file to You under the Apache License, Version 2.0
+# (the "License"); you may not use this file except in compliance with
+# the License.  You may obtain a copy of the License at
+#
+#    http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+while read -r line; do
+    val=$(echo "$line" | awk '{print $3}')
+    if   [[ $line =~ __clang__ ]]; then
+        CLANG=${val}
+    elif [[ $line =~ __GNUC__ ]]; then
+        GNUC=${val}
+    elif [[ $line =~ __GNUC_MINOR__ ]]; then
+        GNUC_MINOR=${val}
+    elif [[ $line =~ __GNUC_PATCHLEVEL__ ]]; then
+        GNUC_PATCHLEVEL=${val}
+    fi
+done < <("${CXX:-c++}" -dM -E - < /dev/null | grep "__clang__\|__GNUC__\|__GNUC_MINOR__\|__GNUC_PATCHLEVEL__")
+
+if [ -n "$GNUC" ] && [ -n "$GNUC_MINOR" ] && [ -n "$GNUC_PATCHLEVEL" ]; then
+    # Calculate GCC/Clang version
+    GCC_VERSION=$((GNUC * 10000 + GNUC_MINOR * 100 + GNUC_PATCHLEVEL))
+    if [ -n "$CLANG" ] && [ "40000" -lt $GCC_VERSION ] && [ $GCC_VERSION -lt "40800" ]; then
+        # Make version of clang >= 4.8 so that it's not rejected by config_brpc.sh
+        GCC_VERSION=40800
+    fi
+    echo $GCC_VERSION
+else
+    echo 0
+fi