Don't import execinfo.h when not necessary

Author: tnipen

src/api/util.cpp

@@ -5,12 +5,16 @@
 #include <cmath>
 #include <math.h>
 #include <assert.h>
-#include <execinfo.h>
 #include <signal.h>
 #include <iomanip>
 #include <cstdio>
 #include <exception>
 
+#ifdef DEBUG
+// This is not portable (only available on GNU/Linux
+#include <execinfo.h>
+#if
+
 using namespace gridpp;
 
 bool gridpp::is_valid(float value) {