aco: don't create sendmsg(dealloc_vgprs) if scratch is used

LLVM does something similar: https://reviews.llvm.org/D153295

fossil-db (gfx1100):
Totals from 21 (0.02% of 133461) affected shaders:
Instrs: 147428 -> 147396 (-0.02%)
CodeSize: 797188 -> 797060 (-0.02%)

Signed-off-by: Rhys Perry <pendingchaos02@gmail.com>
Reviewed-by: Daniel Schürmann <daniel@schuermann.dev>
Fixes: 2930317cea ("aco/gfx11: deallocate VGPRs at the end of the shader")
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/24669>

src/amd/compiler/aco_ir.cpp

@@ -1345,6 +1345,11 @@ dealloc_vgprs(Program* program)
    if (program->max_reg_demand.vgpr <= get_addr_vgpr_from_waves(program, max_waves))
       return false;
 
+   /* sendmsg(dealloc_vgprs) releases scratch, so this isn't safe if there is a in-progress scratch
+    * store. */
+   if (uses_scratch(program))
+      return false;
+
    Block& block = program->blocks.back();
 
    /* don't bother checking if there is a pending VMEM store or export: there almost always is */