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 84.21%. Comparing base (9fd58f9) to head (a44818e).

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #1190   +/-   ##
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  Coverage   84.21%   84.21%           
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  Files          57       57           
  Lines        5973     5973           
=======================================
  Hits         5030     5030           
  Misses        943      943           

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