There's no explicit support, but gcc is tremendously configurable and can easily be used to create code that uses the extra RAM pages provided by the SAMS (in much the same way that it can be used to create code for bankswitching carts, I created a thread on that last year explaining how I did it). All it would require is a little inline assembly to do the page switching (I believe page switching is CRU based on the SAMS? If it's 'memory mapped' like a cart you don't even need assembly).
Having said that, it would be awesome if the compiler could natively support bankswitched memory (both SAMS and latching carts), making it so that one wouldn't have to explicitly switch banks and copy state when running code in another bank (via so-called trampoline functions). The non-standard concept of 'far pointers' in the old DOS days was introduced to do exactly that. Not sure how feasible it is to add that the the tms9900 backend in gcc though .
*edit* but the short answer is 'yes', you can use SAMS memory in gcc programs .
Edited by TheMole, Wed May 25, 2016 3:07 PM.