add build helper script

- use clang as default compiler
- add depends check
- use split build directory for gcc/clang

build2.sh

@@ -0,0 +1,70 @@
+#!/bin/bash
+
+cmake_flags=(
+    # CMAKE_BUILD_TYPE
+    # values: Release/Debug
+    -DCMAKE_BUILD_TYPE=Release
+
+    # CMAKE_VERBOSE_MAKEFILE
+    # ON: verbose build output, OFF: silent build output
+    -DCMAKE_VERBOSE_MAKEFILE=ON
+
+    -DOB_BUILD_RPM=OFF
+
+    # OB_USE_CLANG
+    # ON: use clang, OFF: use gcc
+    -DOB_USE_CLANG=ON
+
+    # OB_USE_LLVM_LIBTOOLS
+    # ON: use lld & llvm-objcopy, OFF: use ld & objcopy
+    -DOB_USE_LLVM_LIBTOOLS=ON
+
+    -DOB_COMPRESS_DEBUG_SECTIONS=OFF
+    -DOB_STATIC_LINK_LGPL_DEPS=OFF
+
+    -DOB_USE_CCACHE=OFF
+    -DOB_ENABLE_PCH=ON
+    -DOB_ENALBE_UNITY=ON
+    -DOB_MAX_UNITY_BATCH_SIZE=30
+    -DOB_USE_ASAN=OFF
+
+    -DOB_RELEASEID=1
+)
+
+# check the depends library
+for i in openssl RapidJSON libisal; do
+    pkg-config --exists $i
+    if [ $? -ne 0 ];then
+        echo "Please install $i"
+        exit
+    fi
+done
+
+# use split build directory for gcc/clang (release/debug)
+BUILD_DIR=build
+eval "export `echo "${cmake_flags[@]}" | sed 's/\-D//g'`"
+if [ $OB_USE_CLANG == "ON" ]; then
+  BUILD_DIR="${BUILD_DIR}.clang"
+elif [ $OB_USE_CLANG == "OFF" ]; then
+  BUILD_DIR="${BUILD_DIR}.gcc"
+fi
+
+if [ $OB_USE_LLVM_LIBTOOLS == "ON" ]; then
+  BUILD_DIR="${BUILD_DIR}.lld"
+elif [ $OB_USE_LLVM_LIBTOOLS == "OFF" ]; then
+  BUILD_DIR="${BUILD_DIR}.ld"
+fi
+
+if [ $CMAKE_BUILD_TYPE == "Release" ];then
+  BUILD_DIR="${BUILD_DIR}.release"
+elif [ $CMAKE_BUILD_TYPE == "Debug" ];then
+  BUILD_DIR="${BUILD_DIR}.debug"
+fi
+eval "unset `echo "${cmake_flags[@]}" | sed 's/\-D//g' | sed 's/=[0-9a-zA-Z]*/ /g'`"
+
+[ -d $BUILD_DIR ] || mkdir -p $BUILD_DIR
+cd $BUILD_DIR
+
+cmake "${cmake_flags[@]}" ..
+
+make -j`nproc` 2>&1 | tee build.log