CMakeLists.txt: Do not require C++ (#3956)

By default, the project() CMake command defaults to C and C++. [1]
Therefore, CMake might perform tests for both C and C++ compilers as
part of the configuration phase.

However, this has the consequence of the configuration phase to fail if
the system does not have a C++ toolchain installed, even if C++ is not
really used by the top-level project under the default settings.

Some configurations might still require a C++ toolchain, so
enable_language is selectively called under such circumstances.

[1]: https://cmake.org/cmake/help/latest/command/project.html

core/iwasm/compilation/iwasm_compl.cmake

@@ -1,6 +1,7 @@
 set (IWASM_COMPL_DIR ${CMAKE_CURRENT_LIST_DIR})
 
 include_directories(${IWASM_COMPL_DIR})
+enable_language(CXX)
 
 if (WAMR_BUILD_DEBUG_AOT EQUAL 1)
     file (GLOB_RECURSE source_all