change include path to build on linux, fix .gitignore

test/.gitignore

@@ -4,5 +4,6 @@
 /test-double
 /test-double-system
 /test-double.dSYM
-/libm-bench
+/bench-openlibm
+/bench-syslibm
 /*.exe

test/libm-bench.cpp

@@ -3,7 +3,7 @@
 // Benchmark on libm functions
 
 #include <math.h>
-#include <sys/time.h>
+#include <time.h>
 #include <stdio.h>
 #include <stdlib.h>