build: do not use LTO for --perf

LTO results in a significant performance boost, but hurts debugability of the results from perf. For now, disable it.

configure

@@ -65,9 +65,9 @@ if [[ "$coverage" == "yes" ]]; then
     ldflags_extra="$ldflags_extra -lgcov --coverage"
 fi
 
-release_cflags="-O3 -flto"
+release_cflags="-O3"
 if [[ "$release" == "yes" ]]; then
-    ccflags_extra="$ccflags_extra $release_cflags"
+    ccflags_extra="$ccflags_extra $release_cflags -flto"
 fi
 
 if [[ "$perf" == "yes" ]]; then