Compile with -fno-common
https://github.com/ggreer/the_silver_searcher/commit/21eaa1c4160b868b0c5bbf59da17974429f30055

Index: src/log.h
--- src/log.h.orig
+++ src/log.h
@@ -9,7 +9,7 @@
 #include <pthread.h>
 #endif
 
-pthread_mutex_t print_mtx;
+extern pthread_mutex_t print_mtx;
 
 enum log_level {
     LOG_LEVEL_DEBUG = 10,
