glsl: replace some C++ code with C

glsl: replace some C++ code with C

This replaces some new/delete uses with malloc/free.

This is more consistent with most of the other glsl IR code but
more importantly it allows the game "Battle Block Theater" to
start working on some mesa drivers. The game overrides new and
ends up throwing an assert and crashing when it sees this
function calling new [0].

Note: The game still crashes with radeonsi due to similar conflicts
with LLVM.

CC: mesa-stable
Reviewed-by: Ian Romanick <ian.d.romanick@intel.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/11907>