Disable some components in llvm build script to decrease binary size (#330)

wamr-compiler/build_llvm.sh

@@ -27,8 +27,11 @@ if [ ! -f bin/llvm-lto ]; then
   cmake ../llvm \
           -DCMAKE_EXPORT_COMPILE_COMMANDS=ON \
           -DCMAKE_BUILD_TYPE:STRING="Release" \
+          -DLLVM_TARGETS_TO_BUILD:STRING="X86;ARM;AArch64;Mips" \
           -DLLVM_BUILD_LLVM_DYLIB:BOOL=OFF \
           -DLLVM_OPTIMIZED_TABLEGEN:BOOL=ON \
+          -DLLVM_ENABLE_ZLIB:BOOL=OFF \
+          -DLLVM_INCLUDE_DOCS:BOOL=OFF \
           -DLLVM_INCLUDE_EXAMPLES:BOOL=OFF \
           -DLLVM_INCLUDE_TESTS:BOOL=OFF \
           -DLLVM_INCLUDE_BENCHMARKS:BOOL=OFF \