Add checks to avoid wasm_runtime_malloc memory with size 0 (#507)

In some platforms, allocating memory with size 0 may return NULL but not an empty memory block, which causes runtime load, instantiate or execute wasm/aot file failed. We add checks to try to avoid allocating memory in runtime if the size is 0. And in wasm_runtime_malloc/free, output warning if allocate memory with size 0 and free memory with NULL ptr.
Also fix some coding style issues, fix handle riscv32 ilp32d issue, and fix several wasm-c-api issues.

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

samples/workload/meshoptimizer/codecbench.patch

@@ -1,5 +1,5 @@
 diff --git a/CMakeLists.txt b/CMakeLists.txt
-index ffdb4da..536a5c8 100644
+index ffdb4da..a397427 100644
 --- a/CMakeLists.txt
 +++ b/CMakeLists.txt
 @@ -127,3 +127,43 @@ install(FILES
@@ -24,7 +24,7 @@ index ffdb4da..536a5c8 100644
 +
 +target_link_options(codecbench
 +  PUBLIC
-+    LINKER:-allow-undefined,--demangle
++    LINKER:-allow-undefined,--demangle,--export=malloc,--export=free
 +)
 +
 +find_program(WASM_OPT