[magma] Fix build with magma_enable_tracing=false

There's some bit rot in this untested configuration.

Test: fx set arm64 --args=magma_enable_tracing=false --available garnet/packages/kitchen_sink && fx full-build
Change-Id: Ibdf645cccbb484964b6da11343ebe45c52743ad4
diff --git a/garnet/drivers/gpu/msd-arm-mali/src/job_scheduler.cc b/garnet/drivers/gpu/msd-arm-mali/src/job_scheduler.cc
index 879c9b1..5b4d203 100644
--- a/garnet/drivers/gpu/msd-arm-mali/src/job_scheduler.cc
+++ b/garnet/drivers/gpu/msd-arm-mali/src/job_scheduler.cc
@@ -21,7 +21,7 @@
 
 // Use different names for different slots so they'll line up cleanly in the
 // trace viewer.
-static const char* AtomRunningString(uint32_t slot)
+[[maybe_unused]] static const char* AtomRunningString(uint32_t slot)
 {
     switch (slot) {
         case 0:
@@ -201,7 +201,8 @@
         executing_atoms_[slot] = atom;
         runnable.erase(runnable.begin());
         std::shared_ptr<MsdArmConnection> connection = atom->connection().lock();
-        msd_client_id_t id = connection ? connection->client_id() : 0;
+        [[maybe_unused]] msd_client_id_t id =
+            connection ? connection->client_id() : 0;
         TRACE_ASYNC_BEGIN("magma", AtomRunningString(slot), executing_atoms_[slot]->trace_nonce(),
                           "id", id);
         owner_->RunAtom(executing_atoms_[slot].get());
diff --git a/garnet/lib/magma/src/magma_util/platform/zircon/zircon_platform_trace.cc b/garnet/lib/magma/src/magma_util/platform/zircon/zircon_platform_trace.cc
index 627874f..9e0af9a 100644
--- a/garnet/lib/magma/src/magma_util/platform/zircon/zircon_platform_trace.cc
+++ b/garnet/lib/magma/src/magma_util/platform/zircon/zircon_platform_trace.cc
@@ -4,9 +4,9 @@
 
 #include "zircon_platform_trace.h"
 
-#include <memory>
-
 #include <lib/fit/function.h>
+#include <memory>
+#include <zircon/syscalls.h>
 
 #include "magma_util/dlog.h"
 #include "magma_util/macros.h"