For what GCC and GCC-compatible compilers use __attribute__ most other compilers use #pragma directives.
I think GCC’s solution is better since the required behavior of an unrecognised #pragma is to ignore it, whereas if you use a compiler that does not understand an __attribute__ specification, it will not compile – which is generally better, since you then know what you need to port.
Attribute specifications are used to specify aspects of types, data, and functions such as storage and alignment that cannot be specified using C. Often these are target specific, mostly they are non-portable, certainly between compilers, and often between targets. Avoid their use except where it is absolutely necessary to use correct functions of code.