Change include guards in quantum/ to pragma once (#11239)

quantum/variable_trace.h

@@ -14,8 +14,7 @@
  * along with this program.  If not, see <http://www.gnu.org/licenses/>.
  */
 
-#ifndef VARIABLE_TRACE_H
-#define VARIABLE_TRACE_H
+#pragma once
 
 // For more information about the variable tracing see the readme.
 
@@ -46,4 +45,3 @@
 void add_traced_variable(const char* name, void* addr, unsigned size, const char* func, int line);
 void remove_traced_variable(const char* name, const char* func, int line);
 void verify_traced_variables(const char* func, int line);
-#endif