CLAMR: Add missing include wrt struct timeval for musl

With musl, mesh.cpp compilation fails as struct timeval is not defined
although <time.h> is included before "timer.h" which uses this data
type.

The reason is with musl contrary to glibc, <time.h> does not include
<sys/time.h> (which provides gettimeofday, struct timeval).

Fixes llvm/llvm-project#94320

MultiSource/Benchmarks/DOE-ProxyApps-C++/CLAMR/timer.h

@@ -56,6 +56,8 @@
 #ifndef _TIMER_H
 #define _TIMER_H
 
+#include <sys/time.h>
+
 #ifdef __cplusplus
 extern "C"
 {