Update build scripts and documents of workload samples for wasi-sdk-12.0 (#484)

Update the build scripts of sample workloads (meshoptimizer/bwa/wasm-av1) to use the wasi-sdk-12.0 firstly to build the workload and discard clang-11, as wasi-sdk-12 supports wasi, simd and pthread better. And update the related documents.
Also modify wasm mini loader to sync up with the change of wasm normal loader.

Signed-off-by: Wenyong Huang <wenyong.huang@intel.com>

samples/workload/cmake/toolchain.cmake

@@ -1,102 +0,0 @@
-# Copyright (C) 2019 Intel Corporation. All rights reserved.
-# SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
-
-cmake_minimum_required (VERSION 3.0)
-
-if(DEFINED _WAMR_TOOLCHAIN_CMAKE_)
-  return()
-else()
-  set(_WAMR_TOOLCHAIN_CMAKE_ 1)
-endif()
-
-SET(CMAKE_SYSTEM_NAME Linux)
-
-################  COMPILER  ################
-find_program(CLANG_11 NAMES clang clang-11 REQUIRED)
-find_program(CLANG++_11 NAMES clang++ clang++-11 REQUIRED)
-
-if(NOT CLANG_11)
-  message(FATAL_ERROR "clang not found")
-else()
-  message(STATUS "use ${CLANG_11} as the c compiler")
-endif()
-
-if(NOT CLANG++_11)
-  message(FATAL_ERROR "clang++ not found")
-else()
-  message(STATUS "use ${CLANG++_11} as the c++ compiler")
-endif()
-
-set(CMAKE_C_COMPILER "${CLANG_11}" CACHE STRING "C compiler" FORCE)
-set(CMAKE_C_COMPILER_ID Clang CACHE STRING "C compiler ID" FORCE)
-
-set(CMAKE_CXX_COMPILER "${CLANG++_11}" CACHE STRING "C++ compiler" FORCE)
-set(CMAKE_CXX_COMPILER_ID Clang CACHE STRING "C++ compiler ID" FORCE)
-
-################  WASI AS SYSROOT  ################
-find_path(WASI_SYSROOT
-  wasi-sysroot
-  PATHS /opt/wasi-sdk-11.0/share /opt/wasi-sdk/share
-  REQUIRED
-)
-
-if(NOT WASI_SYSROOT)
-  message(FATAL_ERROR
-    "can not find wasi sysroot. "
-    "please download it from "
-    "https://github.com/WebAssembly/wasi-sdk/releases/download/wasi-sdk-11/wasi-sdk-11.0-linux.tar.gz "
-    "and install it under /opt"
-  )
-endif()
-
-set(CMAKE_SYSROOT ${WASI_SYSROOT}/wasi-sysroot CACHE STRING "--sysroot to compiler" FORCE)
-
-add_compile_options(
-  --target=wasm32-wasi
-  -msimd128
-  $<IF:$<CONFIG:Debug>,-O0,-O3>
-  $<$<CONFIG:Debug>:-g>
-  $<$<CONFIG:Debug>:-v>
-)
-
-# need users to create their own additional include files
-
-################  AR  ################
-find_program(LLVM_AR NAMES llvm-ar llvm-ar-11 REQUIRED)
-
-if(NOT LLVM_AR)
-  message(FATAL_ERROR "llvm-ar not found")
-else()
-  message(STATUS "use ${LLVM_AR} as the AR")
-endif()
-
-set(CMAKE_AR "${LLVM_AR}" CACHE STRING "AR" FORCE)
-
-################  RANLIB  ################
-find_program(LLVM_RANLIB NAMES llvm-ranlib llvm-ranlib-11 REQUIRED)
-
-if(NOT LLVM_RANLIB)
-  message(FATAL_ERROR "llvm-ranlib not found")
-else()
-  message(STATUS "use ${LLVM_RANLIB} as the ranlib")
-endif()
-
-set(CMAKE_RANLIB "${LLVM_RANLIB}" CACHE STRING "RANLIB" FORCE)
-
-################  LD  ################
-find_program(WASM_LD NAMES wasm-ld wasm-ld-11 REQUIRED)
-
-if(NOT WASM_LD)
-  message(FATAL_ERROR "wasm-ld not found")
-else()
-  message(STATUS "use ${WASM_LD} as the linker")
-endif()
-
-add_link_options(
-  --target=wasm32-wasi
-  -fuse-ld=${WASM_LD}
-  LINKER:--allow-undefined
-  $<IF:$<CONFIG:Debug>,-O0,-O3>
-  $<$<CONFIG:Debug>:-g>
-  $<$<CONFIG:Debug>:-v>
-)