Link libraries explicitly

pthread and libmath are linked implicitly when linking sanitizers. If
NO_SANITIZERS is 1, this will lead to a linker error due to the missing
libraries.

Makefile

@@ -153,6 +153,7 @@ ifneq ($(NO_WARN_FAIL),1)
 endif
 CFLAGS_linux += -ggdb
 CFLAGS_linux += -DFFMPEG_DECODING
+LFLAGS_linux += -pthread -lm
 
 # for now enable extensive error checking
 # Add flags for extensive error checking if NO_SANITIZERS is not set to 1