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/meshoptimizer/codecbench.patch

@@ -1,8 +1,8 @@
 diff --git a/CMakeLists.txt b/CMakeLists.txt
-index eccc49e..dac126c 100644
+index ffdb4da..536a5c8 100644
 --- a/CMakeLists.txt
 +++ b/CMakeLists.txt
-@@ -127,3 +127,42 @@ install(FILES
+@@ -127,3 +127,43 @@ install(FILES
      ${CMAKE_CURRENT_BINARY_DIR}/meshoptimizerConfig.cmake
      ${CMAKE_CURRENT_BINARY_DIR}/meshoptimizerConfigVersion.cmake
      DESTINATION ${CMAKE_INSTALL_LIBDIR}/cmake/meshoptimizer)
@@ -16,6 +16,7 @@ index eccc49e..dac126c 100644
 +
 +target_compile_options(codecbench
 +  PUBLIC
++    -O3 -msimd128
 +    -std=c++11
 +    -Wno-unused-function
 +    -Wno-unused-variable