c: Fix compile errors when vector init is used in a macro

On some platforms, memcpy is a macro. Example: Raspberry Pi RP2040. In this case, the commas inside the array initializer gets mis-interpreted as macro argument separators. Adding an outer parenthesis fixes this issue. Fixes compile errors with trees, on form .../model_m2cgen.h:5343:115: error: macro "memcpy" passed 8 arguments, but takes just 3 5343 | memcpy(var19, (double[]){0.0, 0.0, 0.0, 0.0, 1.0, 0.0}, 6 * sizeof(double)); | ^ .../zephyr-sdk-0.16.5/arm-zephyr-eabi/picolibc/include/ssp/string.h:97: note: macro "memcpy" defined here 97 | #define memcpy(dst, src, len) __ssp_bos_check3(memcpy, dst, src, len)