Support sanitizer for C++ projects

[sfod]

Issue #, and/or reason for changes (REQUIRED):

aws_check_sanitizer checks for the sanitizer flags using check_c_compiler_flag. However, C language might be disabled for C++ projects, which leads to the following error:

CMake Error at /usr/share/cmake3/Modules/CheckCSourceCompiles.cmake:109 (try_compile):
  Unknown extension ".c" for file
    aws-iot-device-sdk-cpp-v2/samples/mqtt5/mqtt5_pubsub/cmake-build-tsan/CMakeFiles/CMakeTmp/src.c
  try_compile() works only for enabled languages.  Currently these are:
    CXX
  See project() command to enable other languages.

Description of changes:

Add check for C++ compiler.
Check compiler flags only if corresponding language is enabled.

If both C and C++ compilers are not loaded, no check_*_compiler_flag function will be called and sanitizer won't be enabled. In a way, it's similar to current logic: when C compiler doesn't support a specified sanitizer check, cmake simply doesn't add corresponding compiler flags.

CMAKE_CXX_COMPILER_LOADED and CMAKE_C_COMPILER_LOADED are available since at least CMake 3.0.

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 84.24%. Comparing base (8f8b98d) to head (604ef54).
⚠️ Report is 11 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1190      +/-   ##
==========================================
- Coverage   84.25%   84.24%   -0.01%     
==========================================
  Files          57       57              
  Lines        5981     5980       -1     
==========================================
- Hits         5039     5038       -1     
  Misses        942      942              

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