try_compile: Escape CMAKE_<lang>_FLAGS in test projects (#14268)

If CMAKE_<lang>_FLAGS contains quotes or other CMake language characters
they must be escaped when written into the generated CMakeLists.txt file
so that the test project parses them properly.

Teach the TryCompile test to cover this case by adding a flag with
quotes into CMAKE_C_FLAGS during a C language try_compile.
Merge topic 'try_compile-escape-flags' into next

628be3c try_compile: Escape CMAKE_<lang>_FLAGS in test projects (#14268)