Moving USE_PTHREADS define over to mozilla/config/config.mk, more than jpeg needs this.

jpeg/Makefile

@@ -81,8 +81,3 @@ endif
 
 include $(DEPTH)/config/rules.mk
 
-# From nsprpub/config/config.mk, mozilla/jpeg needs to know
-# about USE_PTHREADS.  This fixes platforms like SparcLinux. -mcafee
-ifeq ($(USE_PTHREADS), 1)
-OS_CFLAGS += -D_PR_PTHREADS -UHAVE_CVAR_BUILT_ON_SEM
-endif